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Lake Tahoe Basin Water Level Assessment and 2026 Drought Impact Forecast

Strategic Hydrological Intelligence Report

Analysis Date: February 17, 2026
Region: Lake Tahoe Basin, California-Nevada (Sierra Nevada)
Bounding Box (AOI): [[[-120.25, 38.85], [-119.85, 38.85], [-119.85, 39.35], [-120.25, 39.35], [-120.25, 38.85]]]
Center Coordinates: -120.0°W, 39.1°N
Temporal Scope: Water Year 2026 (October 1, 2025 – September 30, 2026)

Executive Summary: Lake Tahoe Basin Demonstrates Resilience—Drought Risk for 2026 is LOW

The Lake Tahoe Basin enters the critical spring snowmelt period of Water Year 2026 in a position of hydrological strength. This comprehensive analysis, integrating satellite-derived spectral indices, ERA5-Land reanalysis precipitation data, MODIS snow cover observations, and probabilistic forecasting models, delivers an unambiguous conclusion: the Lake Tahoe Basin faces low drought risk for the 2026 season, with water levels projected to remain within the legally mandated operating range of [6,223.0 to 6,229.1 feet](Tahoe Regional Planning Agency regulatory framework). The quantitative evidence supporting this assessment is compelling. October-January precipitation for Water Year 2026 registered at [476.6 mm](ERA5-Land Monthly Aggregates, October 2025-January 2026), representing [97.9% of the expected normal](calculated as observed/expected where expected = 885.0 mm × 0.55 seasonal ratio). More critically, snow cover across the basin measured [696.1 km²](MODIS MOD10A1 NDSI analysis, January-February 2026, 42 observations) during January-February 2026—a robust [125.3% of the historical average](computed against 555.56 km² baseline, 2020-2025). This above-normal snowpack provides a substantial hydrological buffer, ensuring adequate spring and summer inflows to maintain lake levels. The Combined Drought Index, calculated using a weighted formula of precipitation anomaly (60%) and snow cover anomaly (40%), yields a value of [+0.54](0.6 × (-0.048) + 0.4 × 1.43), classifying current conditions as "Moderately Wet" with no drought conditions present. This stands in stark contrast to the exceptional drought year of 2020, when precipitation plummeted to [558.1 mm](ERA5-Land annual total, 2020)—just [63% of the long-term average](558.1/885.0 × 100). Probabilistic scenario modeling projects Water Year 2026 total precipitation at a weighted average of [836.0 mm](scenario-weighted calculation: 755.4×0.25 + 815.1×0.30 + 874.8×0.30 + 934.6×0.15), representing [94% of normal](836.0/885.0 × 100). Even under the driest modeled scenario (25% probability), precipitation would reach [755.4 mm](dry scenario: historical average × remaining season factor 0.70), still delivering [85% of normal](755.4/885.0 × 100)—far above thresholds that would trigger significant water supply concerns or measurable drought impacts. The strategic implications for water managers, regional planners, municipal authorities, and recreational stakeholders are clear: no emergency drought measures are warranted for 2026. Lake level impacts are projected at a negligible [-0.03 feet](precipitation deficit × conversion factor: (-10.1/100) × 0.3), well within natural variation. Wildfire risk—a critical concern given recent California fire seasons—registers as [LOW](NDVI anomaly +0.14 indicates above-normal vegetation health). Public sentiment monitoring confirms this favorable outlook, with California water authorities reporting the state is

and reservoirs operating at

. This report provides the evidentiary foundation for confident decision-making across water resource planning, agricultural operations, recreational management, and ecosystem stewardship for the Lake Tahoe Basin through the 2026 season.

1. Hydrological Context: Why Lake Tahoe's Water Status Matters Now

The Strategic Importance of the Tahoe Basin

Lake Tahoe occupies a singular position in the water infrastructure of the American West. Straddling the California-Nevada border at an elevation of approximately [6,225 feet](mean lake surface elevation), the lake and its surrounding watershed constitute a critical component of the Truckee River system that ultimately supplies drinking water to Reno-Sparks and agricultural irrigation across western Nevada. The lake's surface area of approximately [495 km²](JRC Global Surface Water dataset) holds an estimated 39 trillion gallons of water, making it the largest alpine lake in North America. The regulatory framework governing Lake Tahoe's water levels—established through interstate compact and federal court decree—mandates that lake levels remain between [6,223.0 and 6,229.1 feet](Tahoe Regional Planning Agency). The lower threshold represents the natural rim at which outflow to the Truckee River ceases entirely, while the upper limit prevents shoreline flooding and structural damage to lakefront properties. Monitoring water inputs—primarily snowmelt from the surrounding Sierra Nevada peaks—enables proactive management of dam operations at the lake's outlet.

The 2026 Decision Context

Water Year 2026 presents unique planning challenges. Following California's historic drought cycles of 2012-2016 and 2020-2021, water managers and policymakers have heightened awareness of drought vulnerability. The question before us—"What are current water levels in the Lake Tahoe Basin, and what drought impacts should we anticipate for 2026?"—demands a rigorous, data-driven assessment that can inform decisions ranging from municipal water allocation to recreational boat launch operations to wildfire prevention budgeting. The stakes extend beyond hydrology. The Tahoe Basin supports a tourism economy generating billions in annual revenue. Low water levels expose lake bottom sediments, impair water quality through increased algal growth, and restrict marina operations. Conversely, excessive snowmelt can overwhelm drainage infrastructure. Accurate forecasting enables optimal preparation across all sectors.

2. Methodological Framework: How We Derived These Findings

Data Sources and Acquisition

This analysis integrates multiple authoritative geospatial datasets accessed through the Google Earth Engine platform: Precipitation Data:

Source: ECMWF ERA5-Land Monthly Aggregates
Variable: total_precipitation_sum
Resolution: ~9 km
Period: January 2020 through January 2026
Methodology: Basin-mean extraction using polygon-based spatial reduction Snow Cover Data:
Source: MODIS MOD10A1 (Version 6.1)
Variable: Normalized Difference Snow Index (NDSI)
Resolution: 500 m
Threshold: NDSI ≥ 40 classified as snow-covered
Period: Winter months (January-April) 2020-2025; January-February 2026 Surface Water Extent:
Source: JRC Global Surface Water v1.4
Variable: Water occurrence (0-100%)
Resolution: 30 m Vegetation and Moisture Indices:
Source: Sentinel-2 L2A Surface Reflectance
Indices: NDVI, NDWI, NDMI
Resolution: 10-20 m The analytical pipeline processes raw imagery through cloud masking, temporal compositing, and spectral index calculation before extracting basin-scale statistics. All calculations were executed on February 17, 2026.

Drought Index Formulation

The Combined Drought Index employed in this analysis synthesizes precipitation and snow cover anomalies into a single interpretable metric:

CDI = 0.6 imes rac{P_{obs} - P_{exp}}{\sigma_P} + 0.4 imes rac{S_{obs} - S_{mean}}{\sigma_S}

Where:

$P_{obs}$ = Observed October-January precipitation (mm)
$P_{exp}$ = Expected October-January precipitation based on historical seasonal ratios
$\sigma_P$ = Historical standard deviation of annual precipitation
$S_{obs}$ = Observed January-February snow cover area (km²)
$S_{mean}$ = Historical mean snow cover area
$\sigma_S$ = Historical standard deviation of snow cover The weighting assigns 60% importance to precipitation (the primary water input) and 40% to snow cover (which determines timing and magnitude of spring runoff). This formulation aligns with operational drought indices used by the California Department of Water Resources.

Forecast Model Structure

The scenario-based probabilistic projection for remaining Water Year 2026 precipitation employs four discrete outcomes:

[object Object], [Scenario methodology from calculations log](derived from historical precipitation patterns and current conditions assessment)

Where ,[object Object], represents scenario probability and ,[object Object], represents projected annual precipitation under scenario ,[object Object],.

3. Current Water Conditions: Lake Tahoe Basin Enters 2026 in Strong Position

October-January Precipitation Assessment

The first four months of Water Year 2026 (October 2025 through January 2026) provide the foundation for annual water supply forecasting. Analysis of ERA5-Land reanalysis data reveals that the Lake Tahoe Basin received [476.6 mm](ERA5-Land Monthly Aggregates, spatial mean over basin polygon) of precipitation during this period. To contextualize this value, we must compare against historical expectations. The basin's long-term average annual precipitation stands at [885.0 mm](calculated mean of 2020-2025 annual totals from ERA5-Land), with a standard deviation of [212.2 mm](standard deviation of six annual values: 558.1, 935.1, 721.8, 1159.0, 956.4, 979.4). Historical patterns indicate that approximately 55% of annual precipitation falls between October and January in the Sierra Nevada, establishing an expected October-January total of:

P_{expected} = 885.0 imes 0.55 = 486.7 ext{ mm}

The observed value of 476.6 mm represents [97.9%](476.6/486.7 × 100) of this expectation—essentially at normal levels. The precipitation anomaly, calculated as:

PA = rac{476.6 - 486.7}{212.2} = -0.048

indicates conditions indistinguishable from the historical mean (within 0.05 standard deviations).

Snow Cover Analysis: The Critical Buffer

Snow cover provides perhaps the most actionable metric for spring water supply forecasting. Unlike precipitation that may fall as rain and immediately runoff, snowpack stores water through winter and releases it gradually during spring and summer months when demand peaks. MODIS MOD10A1 imagery analysis, employing the NDSI threshold methodology (pixels with NDSI ≥ 40 classified as snow-covered), reveals exceptional early-season snowpack for 2026:

This snow cover surplus of 140.5 km² above average represents a substantial water storage buffer. The standardized anomaly of +1.43 places current snowpack in approximately the 92nd percentile of historical observations—an unambiguously favorable position.

The following satellite visualization captures the January 2026 snow extent across the basin:

Combined Drought Index: Classification as "Moderately Wet"

Integrating precipitation and snow observations into the Combined Drought Index yields:

CDI = 0.6 imes (-0.048) + 0.4 imes 1.433 = -0.029 + 0.573 = 0.544

This value of [+0.54](weighted combination calculation) falls within the "Moderately Wet" classification band (0.5 to 1.0), indicating:

No drought conditions are present
Water supply indicators are favorable
No emergency management actions required The following gauge visualization illustrates the current position:
Figure 2: Current drought index position (black marker at +0.54) on the severity scale. The index falls in the green "Moderately Wet" zone, confirming no drought conditions for the Lake Tahoe Basin as of February 2026.

4. Historical Context: Understanding Tahoe's Hydrological Variability

Six-Year Precipitation Record (2020-2025)

The Lake Tahoe Basin has experienced dramatic interannual variability over the past six years, providing essential context for interpreting 2026 conditions:

This record reveals a system capable of rapid transitions between extreme states. The 2020 drought—with precipitation just ,[object Object],—gave way within three years to the 2023 water year's exceptional ,[object Object],, a swing of nearly 600 mm representing a doubling of annual water input.

Snow Cover Variability Patterns

Snow cover exhibits similarly pronounced variability, though the pattern does not perfectly correlate with precipitation totals due to temperature effects on snow accumulation:

The 2022 observation is particularly instructive: despite below-normal precipitation (82% of average), snow cover reached 129% of normal, suggesting colder temperatures preserved more precipitation as snow rather than rain. Temperature effects matter significantly for water supply timing and magnitude.

Temperature Trends and Evaporative Demand

Annual average temperature for the basin shows no clear trend over the 2020-2025 period, fluctuating around the mean of [7.9°C](ERA5-Land 2m temperature average):

The coolest year (2023) coincided with the wettest year, a pattern consistent with increased cloud cover and precipitation reducing solar heating. For water supply, cooler temperatures reduce evaporative losses and maintain snow longer into spring.

5. 2026 Season Forecast: Probabilistic Projections Signal Continued Favorable Conditions

Scenario-Based Precipitation Outlook

With October-January precipitation accounting for approximately 55% of the water year total, the remaining February-September period must deliver the balance. Our scenario model projects four discrete outcomes:

[object Object], [Scenario methodology from model documentation](probabilistic projection based on historical variability patterns)

This projection of [836.0 mm](scenario-weighted calculation) represents [94% of the historical average](836.0/885.0 × 100)—a mild deficit that poses no significant drought risk.

Critically, even the driest scenario (25% probability) yields [755.4 mm](dry scenario calculation), which would still exceed 2020's extreme drought total of ,[object Object], by nearly 200 mm. The probability of drought conditions matching 2020's severity is essentially zero given current snowpack levels.

Lake Level Impact Assessment

Converting precipitation projections to lake level impacts requires understanding the Tahoe system's hydrology. The simplified water balance model employs:

\Delta L = rac{P_{deficit}}{100} imes 0.3 ext{ ft}

Where 100 mm of precipitation anomaly corresponds to approximately 0.3 feet of lake level change (derived from basin area, lake area, and runoff coefficients). Current precipitation deficit:

P_{deficit} = 476.6 - 486.7 = -10.1 ext{ mm}

Estimated level change:

\Delta L = rac{-10.1}{100} imes 0.3 = -0.03 ext{ ft}

This projected decline of [0.03 feet](water balance calculation)—approximately 0.4 inches—is negligible within the context of natural lake level fluctuations (annual range typically 4-6 feet) and the legal operating range of [6,223.0 to 6,229.1 feet](Tahoe regulatory framework). Impact Assessment: LOW — Lake levels will remain well within normal operating parameters throughout 2026.

6. Vegetation Health and Wildfire Risk: Collateral Benefits of Adequate Water

Spectral Index Analysis

Beyond direct water supply metrics, satellite-derived vegetation indices reveal ecosystem response to current moisture conditions:

The positive NDVI anomaly of [+0.1424](vegetation analysis) indicates vegetation across the basin is healthier than the historical average, a direct consequence of favorable precipitation in recent years (2023-2025 all exceeded normal).

Wildfire Risk Classification

The combination of above-normal snowpack and healthy vegetation translates directly to reduced wildfire risk: Wildfire Risk Assessment: LOW

Key factors:

[125.3%](MODIS snow analysis) of normal snow cover delays fire season onset
[+0.14 NDVI anomaly](Sentinel-2 analysis) indicates vegetation is not stressed
Soil moisture levels adequate based on NDMI readings This assessment should inform fire prevention resource allocation, potentially allowing redeployment of assets to higher-risk regions of California during the 2026 fire season.
Figure 8: Multi-sector risk assessment for the Lake Tahoe Basin. All categories—including water supply, lake levels, wildfire, agriculture, recreation, and ecosystem health—register at LOW or LOW-MODERATE risk levels for 2026.

7. Public Sentiment and Official Reporting: External Validation of Favorable Conditions

Social Media Intelligence

Analysis of public discourse on X (Twitter) corroborates the quantitative findings. Official water management accounts and public commentators reflect optimism about California's 2026 water outlook: Key Public Sentiment Findings:

"California is currently 100% drought-free, with reservoirs at 114-131% of historical averages and strong Sierra Nevada snowpack building from recent storms." —
"Lake Tahoe specifically is benefiting from heavy snowfall forecasts, including 4-5 feet expected at nearby UC Berkeley Central Sierra Snow Lab and up to 8 feet at Donner Pass this week." —
"Earlier low snowpack concerns in mid-December 2025 have been alleviated by incoming storms." —
"Past predictions of permanent or century-long droughts in California (e.g., from 2015) have not materialized, as this wet winter (120-150% above average precipitation in places) has filled systems." —
Official accounts including
, [@tahoe_weather], and [@NorthTahoePUD] report no shortage alerts, confirming our quantitative assessment.

Regional Context: Colorado River Basin Comparison

While Lake Tahoe and the Sierra Nevada water system demonstrate favorable conditions, other Western water systems face different trajectories. Public reporting notes:

"Drought concerns are focused elsewhere, like the Colorado River Basin (Lake Powell projected to hit minimum power pool by late 2026 at 52% average inflows), but this doesn't directly impact Tahoe, which relies on local Sierra precipitation." —
This geographic distinction is critical: Lake Tahoe's hydrological independence from the Colorado River system means that crisis conditions in Arizona and the lower basin do not affect Tahoe water supply. The Sierra Nevada's moisture source—predominantly Pacific atmospheric rivers—operates on different climatological drivers than the monsoon-dependent Colorado system.

8. Code Implementation: How Satellite Data Was Processed

Snow Cover Extraction Algorithm

The following Python code snippet illustrates the methodology used to extract snow cover statistics from MODIS imagery:


# MODIS Snow Cover Analysis
snow = ee.ImageCollection("MODIS/061/MOD10A1") \
    .filterBounds(aoi) \
    .filterDate('2020-01-01', '2026-02-17')
def get_snow_stats(img):
    ndsi = img.select('NDSI_Snow_Cover')
    # Pixels with NDSI >= 40 classified as snow
    snow_area = ndsi.gte(40).multiply(ee.Image.pixelArea())
    total_snow = snow_area.reduceRegion(
        reducer=ee.Reducer.sum(),
        geometry=aoi,
        scale=500,
        maxPixels=1e9
    ).get('NDSI_Snow_Cover')
    return img.set('snow_area_m2', total_snow)
snow_mapped = snow.map(get_snow_stats)

Plain Language Explanation: This code retrieves MODIS satellite images covering the Lake Tahoe Basin from 2020 through February 2026. For each image, it selects the Normalized Difference Snow Index band and identifies pixels where the value exceeds 40 (the standard threshold indicating snow presence). These snow pixels are converted to area measurements in square meters by multiplying by the pixel area. The reduction operation sums all snow-covered area across the basin to produce a single value (total snow extent in m²) for each observation date. This automated processing of hundreds of satellite images enables robust statistical analysis of snow cover trends.

Precipitation Extraction from ERA5-Land


# ERA5-Land Precipitation Analysis
era5 = ee.ImageCollection("ECMWF/ERA5_LAND/MONTHLY_AGGR") \
    .filterBounds(aoi) \
    .filterDate('2020-01-01', '2026-02-01')
def get_precip(img):
    precip = img.select('total_precipitation_sum')
    mean_precip = precip.reduceRegion(
        reducer=ee.Reducer.mean(),
        geometry=aoi,
        scale=9000,
        maxPixels=1e9
    ).get('total_precipitation_sum')
    return img.set('mean_precip_m', mean_precip)

Plain Language Explanation: This code accesses the ERA5-Land global reanalysis dataset, a comprehensive reconstruction of historical weather variables produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). Monthly precipitation totals are extracted for the Lake Tahoe Basin by selecting the total_precipitation_sum variable and computing the spatial average across all grid cells overlapping the basin polygon. The output is precipitation in meters, later converted to millimeters for reporting. ERA5-Land provides consistent, gap-free precipitation estimates at approximately 9 km resolution.

Combined Drought Index Calculation


# Drought Index Calculation
precip_anomaly = (wy2026_precip - expected_precip) / historical_std

# Result: (476.6 - 486.7) / 212.2 = -0.048
snow_anomaly = (current_snow - historical_mean) / snow_std  

# Result: (696.1 - 555.56) / 98.1 = 1.43
combined_index = 0.6 * precip_anomaly + 0.4 * snow_anomaly

# Result: 0.6 * (-0.048) + 0.4 * 1.43 = 0.544
classification = "Moderately Wet"  # (0.5 to 1.0 range)

Plain Language Explanation: The Combined Drought Index standardizes both precipitation and snow cover observations relative to their historical distributions, then weights them to produce a single interpretable value. A negative value indicates drought conditions; a positive value indicates wetter-than-normal conditions. The value of +0.54 places the basin in the "Moderately Wet" category, confirming no drought.

9. Comprehensive Dashboard: Visual Synthesis of All Indicators

The following multi-panel visualization integrates all key metrics into a single analytical dashboard:

Figure 9: Six-panel dashboard summarizing Lake Tahoe Basin water status for February 2026. Top row shows drought index (moderately wet), precipitation status (98% of normal), and snow cover (125% of normal). Middle panels display multi-year precipitation/snow trends and temperature variations. Bottom panel presents the scenario-based forecast with probability-weighted outcomes. All indicators confirm favorable conditions with low drought risk.

Water Dashboard Detail View

Figure 10: Four-panel water metrics dashboard. Upper-left: October-January precipitation at 477 mm vs expected 487 mm. Upper-right: Snow cover at 696 km² vs historical average of 556 km². Lower-left: Drought index component breakdown. Lower-right: Lake level outlook showing minimal projected change (-0.03 ft) with LOW impact classification.

10. Satellite Imagery Gallery: Visual Evidence of Basin Conditions

True Color Basin Overview

Figure 11: Sentinel-2 natural color composite (RGB: Bands 4, 3, 2) showing Lake Tahoe and surrounding watershed during summer 2025. The deep blue lake, forested slopes, and urbanized areas along the shoreline are clearly visible. This imagery provides geographic context for the analysis.

Water Body Extent Analysis

Figure 12: Normalized Difference Water Index (NDWI) highlighting water body extent. Dark blue indicates permanent water (the lake), while lighter blues and greens show vegetation. The NDWI value of 0.3355 confirms robust water presence and proper lake filling.

Long-Term Water Occurrence

Figure 13: JRC Global Surface Water occurrence map showing the probability of water presence over the historical record. Purple/dark blue areas indicate permanent water bodies; lighter shades show areas with seasonal or intermittent water. The water occurrence mean of 98.02% confirms Lake Tahoe's status as a permanent, stable water body.

Moisture Index for Fire Risk Assessment

Figure 14: Normalized Difference Moisture Index (NDMI) for summer 2025. Green areas indicate high vegetation moisture content (lower fire risk); brown areas show drier vegetation. The basin-wide mean of 0.0537 with a 90th percentile of 0.2695 indicates predominantly healthy moisture levels.

Historical Snow Comparison: Drought Year vs. Wet Year

Figure 15: MODIS snow cover during March-April 2020 (drought year). Note the reduced snow extent compared to wet years, with only 462 km² average coverage.

Figure 16: MODIS snow cover during March-April 2023 (exceptionally wet year). Extensive snow coverage at 624 km² reflects the 131% of normal precipitation received that water year.

Drought Timeline Visualization

Figure 17: Precipitation anomaly timeline (2020-2026) showing standardized deviations from historical mean. The 2020 drought (approximately -1.5σ) and 2023 wet year (+1.3σ) bracket the range of observed variability. The 2026 projection at -0.2σ falls well within the "Near Normal" band.

11. Data Limitations and Confidence Assessment

Acknowledged Uncertainties

While the evidence strongly supports a low-drought-risk assessment for 2026, several limitations warrant acknowledgment: 1. Forecast Model Simplifications

The scenario-based projection model employs simplified assumptions including:

Linear relationship between precipitation and lake level response
Constant evaporation rates (actual evaporation varies with temperature and wind)
Historical seasonal patterns applying to 2026 (climate change may alter timing) Confidence Interval: The projected [836 mm](weighted average) carries an uncertainty band of approximately [±15%](model documentation), corresponding to a range of [710-961 mm](836 × 0.85 to 836 × 1.15). 2. Spatial Resolution Constraints
ERA5-Land precipitation data at ~9 km resolution may not capture fine-scale orographic effects
MODIS snow products at 500 m resolution may miss small snow patches 3. Temporal Limitations
2026 snow cover data spans only January-February; full winter assessment awaits March-April observations
Historical baseline period (2020-2025) is relatively short (6 years), potentially not capturing full climate variability 4. Hydrological Model Uncertainty

The lake level impact estimate of [-0.03 feet](simplified calculation) carries substantial uncertainty ([±50% of estimated change](model documentation)) due to:

Groundwater dynamics not modeled
Truckee River outflow regulation effects not incorporated
Variable infiltration rates

What We Know With High Confidence

Despite these limitations, several findings emerge with high certainty:

Snow cover is unambiguously above normal — At [125.3%](MODIS observation) of historical average with 42 independent satellite observations, this finding is robust.
No drought conditions exist currently — The Combined Drought Index of [+0.54](calculated value) places conditions firmly in the wet category.
Severe drought in 2026 is extremely unlikely — Even the driest scenario projection ([755 mm](25% probability)) exceeds 2020's extreme drought by 35%.
Lake levels face no near-term threat — The negligible projected decline of [0.03 feet](water balance estimate) poses no operational concerns.

12. Strategic Recommendations: Actions for Water Managers and Stakeholders

For Municipal Water Authorities

Recommendation 1: Maintain Standard Operations

No emergency conservation measures or drought contingency plan activation is warranted for 2026. Current reservoir levels and projected inflows support normal water delivery schedules through the 2026 season. Recommendation 2: Continue Monitoring

Maintain heightened surveillance of April 1 snow water equivalent measurements—the traditional peak snowpack date. If April 1 snowpack confirms the current above-normal trajectory, further increase confidence in favorable summer water supply. Recommendation 3: Long-Term Infrastructure Planning

Use the 2026 favorable conditions window to advance deferred maintenance projects on water infrastructure without supply constraints.

For Dam Operators (Tahoe Outlet)

Recommendation 4: Normal Outflow Management

With lake levels projected to remain well within the [6,223-6,229.1 foot](regulatory range) operating band, standard outflow protocols should maintain target levels without special intervention. Recommendation 5: Prepare for Spring Runoff

Above-normal snowpack (125.3%) may produce above-normal spring runoff. Ensure downstream flood management coordination is current for May-June peak runoff period.

For Recreation and Tourism Operators

Recommendation 6: Full Seasonal Operations

Marina operators, boat launch facilities, and lakeside recreation businesses can plan for full seasonal operations without low-water restrictions anticipated in 2026. Recommendation 7: Marketing Confidence

Tourism promotion can emphasize favorable water and snow conditions, particularly for summer lake recreation and late-season skiing dependent on spring snowpack.

For Fire Management Agencies

Recommendation 8: Moderate Resource Positioning

Low wildfire risk classification ([LOW](NDVI anomaly assessment)) suggests the Tahoe Basin is not a 2026 priority deployment zone. Consider redeploying assets to higher-risk regions while maintaining baseline capability. Recommendation 9: Monitor Post-Snowmelt Vegetation

Re-assess fire risk in July 2026 once snow has melted and summer drying patterns establish actual fuel moisture conditions.

For Regional Planners and Policymakers

Recommendation 10: Climate Resilience Investment

The favorable 2026 outlook should not diminish long-term drought resilience planning. Historical variability—from 558 mm in 2020 to [1,159 mm in 2023](exceptional wet)—demonstrates the basin's exposure to wide precipitation swings. Continue investment in storage, conservation, and adaptive infrastructure.

13. Conclusion: A Season of Hydrological Resilience

The Lake Tahoe Basin approaches the 2026 water year's critical spring period from a position of notable strength. The convergence of near-normal early-season precipitation (97.9%), exceptional snow cover (125.3%), and a Combined Drought Index firmly in the "Moderately Wet" classification (+0.54) yields an unambiguous assessment: drought impacts for the 2026 season will be minimal to non-existent. This finding reflects not merely favorable conditions in isolation, but the basin's recovery from the extreme drought of 2020 through a sequence of above-normal water years (2021, 2023, 2024, 2025). The Sierra Nevada's capacity to receive and store massive snowpacks—when atmospheric conditions permit—demonstrates the resilience of this critical water supply system. For decision-makers across water management, recreation, fire prevention, and regional planning domains, the evidence presented in this analysis supports a posture of confident normalcy. No emergency measures are warranted. Standard operations should proceed. Strategic investments in long-term resilience should continue independent of this year's favorable outlook. The Lake Tahoe Basin remains, as it has for millennia, a reliable source of high-quality water for downstream communities—and for 2026, that reliability continues uninterrupted.

Appendix A: Complete Reference List

External Source URLs

California Drought-Free Status Report:
Reservoir Levels Confirmation:
Historical Drought Assessment:
Lake Tahoe Snowfall Forecast:
Snow Lab Projections:
Wet Winter Analysis:
Snowpack Recovery Update:
Colorado River Basin Comparison:
Lake Powell Projection:
Official Tahoe Agency Status:

Data Sources

Geographic Coordinates

Bounding Box: [-120.25, 38.85, -119.85, 39.35]
Center Point: -120.0°W, 39.1°N
Lake Surface Polygon: [-120.15, 38.93, -119.93, 39.25]
Basin GeoJSON: lake_tahoe_basin.geojson

Generated Analytical Assets

Methodology Summary

Historical Baseline Calculation: Six-year (2020-2025) mean and standard deviation from ERA5-Land and MODIS
Current Status Assessment: October 2025-February 2026 observations compared to seasonal expectations
Drought Index Computation: Weighted combination of standardized precipitation and snow anomalies
Probabilistic Forecasting: Four scenarios with probability-weighted average projection
Lake Level Impact Estimation: Simplified water balance with precipitation-to-level conversion factor

Report prepared: February 17, 2026
Analysis Region: Lake Tahoe Basin, California-Nevada
Classification: UNCLASSIFIED - For Decision Support

Key Events

12 insights

California declared 100% drought-free as of February 2026

Lake Tahoe Basin classified as 'Moderately Wet' for Water Year 2026

Above-normal snowpack established by January-February 2026

2020 extreme drought recorded lowest precipitation in 6-year period

Key Metrics

15 metrics

October-January 2026 Precipitation

476.6 mm received, representing 97.9% of expected normal

Snow Cover Area

696.1 km² in Jan-Feb 2026, 125.3% of historical average

Combined Drought Index

+0.54 (Moderately Wet classification)

2026 Projected Annual Precipitation

836.0 mm weighted average, 94% of normal

Lake Level Impact

-0.03 feet projected decline (negligible)

2020 Drought Year Precipitation

558.1 mm, only 63% of average (extreme drought)

Vector Files

1 vector available

Lake Tahoe Basin Watershed Boundary

Vector Dataset

Gallery

10 images

Comprehensive Summary Dashboard - Six-Panel Analysis

Combined Drought Index Gauge - Current Status

Drought Timeline - Precipitation Anomaly (2020-2026)

Annual Precipitation History (2020-2026)

Multi-Sector Risk Assessment Matrix

2026 Forecast Scenario Probabilities

Winter Snow Cover History (2020-2026)

Annual Temperature Trend (2020-2025)

Water Metrics Dashboard - Four-Panel Analysis

Wet/Dry Year Classification Analysis

Satellite Images

9 satellite imagess available

Lake Tahoe Basin - True Color Composite (Summer 2025)

NDWI - Water Body Detection Index

JRC Global Surface Water Occurrence Map

NDVI - Vegetation Health Index (Summer 2024)

NDMI - Vegetation Moisture Index (Summer 2025)

Land Surface Temperature Map (Summer 2025)

MODIS Snow Cover - January 2026 (Current)

MODIS Snow Cover - March 2020 (Drought Year)

MODIS Snow Cover - March 2023 (Wet Year)

Files

21 files available

Scenario	Factor Applied to Historical Avg	Probability	Rationale
Dry	0.70	25%	Below-normal remaining season
Below Normal	0.85	30%	Slightly dry conditions
Normal	1.00	30%	Historical average pattern
Above Normal	1.15	15%	Wetter than normal (less likely given neutral ENSO)
The weighted average projection is computed as:
$\hat{P}_{annual} = \sum_{i=1}^{4} p_i imes P_i$

Metric	Value	Source
Jan-Feb 2026 Average Snow Cover	[696.1 km²](MODIS MOD10A1, 42 observations)	Satellite snow detection
Historical Average (2020-2025)	[555.56 km²](mean of 6-year winter values)	Baseline calculation
Percent of Normal	[125.3%](696.1/555.56 × 100)	Anomaly assessment
Snow Anomaly (standardized)	+1.43	Statistical deviation

Figure 1: MODIS NDSI snow cover classification for January-February 2026, showing extensive snow coverage (white areas) across the Lake Tahoe watershed. Snow-free areas appear in gray/black. The robust snowpack provides strong water supply assurance for the coming spring and summer.

Year	Annual Precipitation (mm)	% of Average	Classification	Source
2020	[558.1](ERA5-Land annual total)	63%	Extreme Drought	Satellite reanalysis
2021	[935.1](ERA5-Land annual total)	106%	Above Normal	Satellite reanalysis
2022	[721.8](ERA5-Land annual total)	82%	Below Normal	Satellite reanalysis
2023	[1,159.0](ERA5-Land annual total)	131%	Exceptionally Wet	Satellite reanalysis
2024	[956.4](ERA5-Land annual total)	108%	Above Normal	Satellite reanalysis
2025	[979.4](ERA5-Land annual total)	111%	Above Normal	Satellite reanalysis

Figure 3: Annual precipitation for Lake Tahoe Basin (2020-2026). Red bars indicate drought years (<700 mm), blue bars show normal years (700-900 mm), and green bars represent wet years (>900 mm). The purple hatched bar shows the 2026 weighted projection of 836 mm. The red dashed line marks the historical average of 885 mm.

Year	Avg Winter Snow Cover (km²)	% of Average	Notes
2020	[462.3](MODIS MOD10A1)	83%	Low—drought year
2021	[537.3](MODIS MOD10A1)	97%	Near normal
2022	[716.8](MODIS MOD10A1)	129%	High despite below-normal precip
2023	[624.1](MODIS MOD10A1)	112%	Above normal
2024	[469.9](MODIS MOD10A1)	85%	Low
2025	[522.9](MODIS MOD10A1)	94%	Near normal
2026	[696.1](MODIS MOD10A1, Jan-Feb)	125%	Excellent early season

Figure 4: Winter snow cover area (2020-2026). The 2026 value represents January-February observations only but already exceeds full-winter averages from most prior years, indicating excellent early-season snowpack.

Year	Avg Temperature (°C)	Anomaly
2020	8.40	+0.5°C (warmer)
2021	8.37	+0.5°C (warmer)
2022	7.66	-0.2°C (cooler)
2023	6.57	-1.3°C (coolest)
2024	8.11	+0.2°C
2025	8.27	+0.4°C

Figure 5: Annual average temperature (2020-2025). The 2023 wet year exhibited notably cooler temperatures (6.57°C), while drought year 2020 was among the warmest (8.40°C).

Scenario	Remaining Season Factor	Projected Total (mm)	% of Normal	Probability
Dry	0.70	[755.4](476.6 + 0.70 × 398.2)	85%	25%
Below Normal	0.85	[815.1](476.6 + 0.85 × 398.2)	92%	30%
Normal	1.00	[874.8](476.6 + 1.00 × 398.2)	99%	30%
Above Normal	1.15	[934.6](476.6 + 1.15 × 398.2)	106%	15%
The weighted average projection:
$\hat{P}_{2026} = (755.4 imes 0.25) + (815.1 imes 0.30) + (874.8 imes 0.30) + (934.6 imes 0.15) = 836.0 ext{ mm}$

Figure 6: Probability distribution for WY2026 precipitation scenarios. The combined probability of normal or above-normal conditions is 45%, while all scenarios remain well above severe drought thresholds.

Index	Value	Interpretation	Source
NDWI (Lake Surface)	[0.3355](Sentinel-2 NDWI calculation)	Healthy water body detection	Spectral analysis
NDVI (Basin Mean)	[0.3651](Sentinel-2 NDVI calculation)	Moderate-good vegetation health	Spectral analysis
NDMI (Summer 2025)	[0.0537](Sentinel-2 NDMI calculation)	Variable moisture content	Spectral analysis
NDVI Anomaly	[+0.1424](2025 vs historical comparison)	Above normal vegetation health	Anomaly calculation

Figure 7: Normalized Difference Vegetation Index (NDVI) for summer 2024. Green areas indicate healthy, photosynthetically active vegetation; yellow/brown areas show stressed or sparse vegetation. The basin exhibits predominantly healthy vegetation.

Dataset	Provider	Access Method	Resolution
ERA5-Land Monthly Aggregates	ECMWF	Google Earth Engine	~9 km
MODIS MOD10A1 Snow Cover	NASA	Google Earth Engine	500 m
JRC Global Surface Water v1.4	European Commission	Google Earth Engine	30 m
Sentinel-2 L2A	ESA/Copernicus	Google Earth Engine	10-20 m
MODIS MOD16A2 Evapotranspiration	NASA	Google Earth Engine	500 m

Filename	Description
`chart_precipitation_history.png`	Annual precipitation bar chart (2020-2026)
`chart_snow_cover_history.png`	Winter snow cover bar chart
`chart_drought_index_gauge.png`	Drought severity gauge visualization
`chart_temperature_trend.png`	Temperature timeline
`chart_scenario_probabilities.png`	Forecast scenario probability distribution
`chart_water_dashboard.png`	Four-panel water metrics dashboard
`chart_comprehensive_summary.png`	Six-panel analytical summary
`chart_risk_assessment.png`	Multi-sector risk matrix
`chart_drought_timeline.png`	Historical drought anomaly timeline
`chart_wet_dry_analysis.png`	Wet/dry year classification
`lake_tahoe_true_color.png`	Sentinel-2 RGB composite
`lake_tahoe_ndwi.png`	Water detection index map
`lake_tahoe_water_occurrence.png`	Long-term water presence map
`lake_tahoe_ndvi_summer2024.png`	Vegetation health map
`lake_tahoe_ndmi_summer2025.png`	Moisture index map
`lake_tahoe_lst_summer2025.png`	Land surface temperature map
`lake_tahoe_snow_cover_jan2026.png`	Current snow coverage
`lake_tahoe_snow_march2020.png`	Drought year snow comparison
`lake_tahoe_snow_march2023.png`	Wet year snow comparison

Key Events

Key Metrics

Vector Files

Lake Tahoe Basin Watershed Boundary

Gallery

Comprehensive Summary Dashboard - Six-Panel Analysis

Combined Drought Index Gauge - Current Status

Drought Timeline - Precipitation Anomaly (2020-2026)

Annual Precipitation History (2020-2026)

Multi-Sector Risk Assessment Matrix

2026 Forecast Scenario Probabilities

Winter Snow Cover History (2020-2026)

Annual Temperature Trend (2020-2025)

Water Metrics Dashboard - Four-Panel Analysis

Wet/Dry Year Classification Analysis

Satellite Images

Lake Tahoe Basin - True Color Composite (Summer 2025)

NDWI - Water Body Detection Index

JRC Global Surface Water Occurrence Map

NDVI - Vegetation Health Index (Summer 2024)

NDMI - Vegetation Moisture Index (Summer 2025)

Land Surface Temperature Map (Summer 2025)

MODIS Snow Cover - January 2026 (Current)

MODIS Snow Cover - March 2020 (Drought Year)

MODIS Snow Cover - March 2023 (Wet Year)

Files

Additional Water Analysis

Calculations Log

Chart Explanations

Context Brief

Date Verification

Drought Prediction Results

Historical Water Data

Key Metrics Summary

Methodology

Model Details

Process Additional

Process Docs

Process Drought

Process Imagery

Process Init

Process Model

Process Viz

Process Viz2

Process Water

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Water Analysis Raw