Understanding the Role of Vegetation Dynamics and Anthropogenic-Induced Changes on the Terrestrial Water Cycle

The land surface and atmosphere interact through complex feedback loops that link energy and water cycles. Effectively characterizing these linkages is critical to modeling weather and climate extremes accurately. Seasonal variability in vegetation growth and human-driven land cover changes (LCC) can alter the biophysical properties of the land surface, which can in turn influence atmosphere and the water cycle. Using a regional-scale climate model (i.e., the Weather Research & Forecasting model), we examine the effect of LCC, irrigation and seasonal variability in vegetation growth on summer water cycle characteristics between the year 2001 and 2015. This study involves utilization of high-resolution satellite derived annual land cover, vegetation properties, and a realistic irrigation scheme with six major crops within the high-resolution regional climate model. Changes in biophysical properties due to LCC reducing the evapotranspiration, atmospheric moisture, and summer precipitation over the contiguous United States (CONUS). The combined effects of LCC and irrigation indicated a significant drying over the CONUS, with increased duration and decreased intensity of dry spells, and reduced duration, frequency, and intensity of wet spells. Irrigated cropland areas will become drier due to the added effect of low-precipitation wet spells and long periods (3-4% increase) of dry days, whereas rainfed croplands are characterized by intense (1-5% increase), short-duration wet spells and long periods of dry days. An analysis based on future climate change projections indicated that 3–4 °C of warming and an intensified water cycle will occur over the CONUS by the end of the 21st century. The results of this study highlight the importance of the accurate representation of seasonal vegetation changes and LCC while forecasting present and future climate.