Abstract
Understanding the patterns and relationships between vegetation productivity and climatic conditions is essential for predicting the future impacts of climate change. Climate change is altering precipitation patterns and increasing temperatures in the Southwest United States. The large-scale and long-term effects of these changes on vegetation productivity are not well understood. This study investigates the patterns and relationships between seasonal vegetation productivity, represented by Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI), and the Standardized Precipitation Evapotranspiration Index (SPEI) across the Mojave, Sonoran, and Chihuahuan Deserts and the Apache Highlands of the Southwest United States over 16 years from 2000 to 2015. To examine the spatiotemporal gradient and response of vegetation productivity to dry and wet conditions, we evaluated the linear trend of different SPEI timescales and correlations between NDVI and SPEI. We found that all four ecoregions are experiencing more frequent and severe drought conditions in recent years as measured by negative SPEI trends and severe negative SPEI values. We found that changes in NDVI were more strongly correlated with winter rather than summer water availability. Investigating correlations by vegetation type across all four ecoregions, we found that grassland and shrubland productivity were more dependent on summer water availability whereas sparse vegetation and forest productivity were more dependent on winter water availability. Our results can inform resource management and enhance our understanding of vegetation vulnerability to climate change.
Highlights
IntroductionThe productivity of vegetation communities is directly impacted by changes in temperature and precipitation, especially in arid and semi-arid regions [1]
April Normalized Difference Vegetation Index (NDVI) Response to Different Standardized Precipitation Evapotranspiration Index (SPEI) Timescales In April we found that the correlation between NDVI and SPEI for the Mojave and Sonoran Deserts was strongest for the 6-month SPEI timescale (Figure 8a)
September NDVI Response to SPEI Timescales In September we found that the correlation between the vegetation productivity and water availability for the Apache Highlands, Chihuahuan, and Sonoran deserts was strongest with the 3-month SPEI timescale (Figure 8a)
Summary
The productivity of vegetation communities is directly impacted by changes in temperature and precipitation, especially in arid and semi-arid regions [1]. United States, for example, the effects of climate change are expected to be pronounced [2]. The frequency, severity, and duration of droughts have increased while water availability has decreased in this region [3]. Trends point to a decline in vegetation productivity due to projected warming and increasingly dry conditions [4,5]. The response of desert vegetation productivity to water availability, variations in the timing, and amount of precipitation varies spatially and temporally [2,6]. The need to understand the relationships between vegetation productivity, precipitation, and drought for these desert ecoregions is
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