2015 West Coast Drought and West - Central U.S. Wet Summer 

METDATA percent of average precipitation, illustrating anomalously low May - July precipitation in California, and high precipitation over the intermountain and central U.S.

Anomalously high spring and summer precipitation led to exceptional rangeland forage conditions over much of the intermountain west and central U.S. See the map below of MODIS vegetation greenness that resulted from anomalously high precipitation during spring and summer of 2015. 


High Vegetation Greenness, Summer of 2015

MODIS May - July, 2015 percent difference from average Normalized Difference Vegetation Index (NDVI)

MODIS percent difference from average NDVI for May - July, 2015 illustrates that much of the intermountain west and central U.S. experienced exceptionally green conditions. Large areas of western Nevada, Wyoming, Colorado, New Mexico, and Texas had 20 to 30 percent above average vegetation greenness.


High Evaporative Demand, Winter of 2015

METDATA January - March, 2015 difference from average reference evapotranspiration

Reference evapotranspiration was exceptionally high from January - March 2015 over much of the western U.S., a result of higher than average solar radiation, air temperature, humidity, and wind speed. These conditions also to a snow drought over much of the western U.S. that compounded drought conditions across California and the Pacific Northwest.


Snow Drought of 2015

MODIS January - March 2015 Normalized Difference Snow Index (NDSI) difference from average 

Snow pack extent, depth, and water content were at record lows in 2015. In the Sierra Nevada and much of the western U.S., April 1 snow water content was only at ~10 percent of normal, leading to one of the worst water supply years on record.


Opposite Drought Signals in Irrigated Areas of Nevada, 2015

Landsat July - August 2015 Normalized Difference Vegetation Index (NDVI) percent difference from average (1985-2015) illustrating drought in irrigated areas of Lovelock, Nevada, due to lack of irrigation water, while at the same time exceptionally green rangeland conditions persisted due to high spring and early summer rain.

The Lovelock Irrigation District, Nevada, has been hit hard by the extended drought of 2013 - 2015. In 2014 and 2015 Lovelock received zero percent of it's normal allotment of irrigation water. Farmers can not pump supplemental groundwater due to saline groundwater, and there is little upstream surface water storage on the Humboldt River. Consequently vegetation greenness in typically irrigated lands was well below normal due to the water curtailment. Conversely, above normal late spring and summer precipitation allowed for enhanced productivity of rain-fed rangelands denoted by the blue hues that show increased greenness. This example illustrates how an area can experience different types of drought (hydrologic vs. rangeland) that can happen at the same time and in opposite directions (no irrigation water, but healthy rangeland conditions due to summer rain).


2015 Fallow Agricultural Land in the San Joaquin Valley, California

Landsat June - August 2015 NDVI percent difference from average (1985-2015) illustrating fallow fields due to the lack of irrigation water

The lack of irrigation water in California during 2015  forced many farmers to fallow land in the San Joaquin Valley. Dark red areas represent 50 percent below average NDVI or more, and represent fallow land. Notice above average NDVI conditions (green) within irrigated areas and along foothill areas. Above average NDVI fields are likely the result of groundwater pumping, and above average summer rain aver foothill areas.


Meteorological Drought of 2014

Palmer Drought Severity Index (PDSI) from April - October 2014, computed using METDATA and physically based Penman-Monteith reference evapotranspiration

Map illustrates PDSI in U.S. Drought Monitor color categories.  Much of central California was in the exceptional drought category of D4 (worst drought category), along with large areas of the central U.S. where the PDSI was below -3.


2014 Southwest U.S. Vegetation Conditions

MODIS July - September 2014 Normalized Difference Vegetation Index (NDVI) percent difference from average illustrating lower than average vegetation greenness over most of California and Nevada, and higher than average greenness over most of southern Arizona and New Mexico

 


2012 Central U.S. Flash Drought: Reduced actual ET and increased reference ET

MODIS land surface temperature difference from average conditions

MODIS land surface temperature (LST) anomalies are especially useful for evaluating drought and vegetation stress.  LST is a function of the evapotranspiration (ET) rate (i.e. latent heat flux). If ET is relatively low, than the LST will be relatively high, and visa versa. This map illustrates increased LST due to reduced ET caused by the lack of soil moisture. Reduced actual ET leads to increased evaporative demand (i.e. reference ET) due to increased air temperature and reduced vapor pressure. This feedback, known as the complementary relationship,  is illustrated in the below example of the reference ET anomaly during this period.

METDATA reference evapotranspiration difference from average conditions

This figure illustrates increased evaporative demand (i.e. reference ET) due to reduced actual ET and increased LST during the flash drought of summer 2012 over the central U.S.