Assessing Land Surface Hydrologic Resilience to Extreme Hydrometeorological Events in Natural and Water-controlled Ecosystems

Our goal is to better understand historical land surface hydrologic responses to hydrometeorological extremes. As in many regions around the world, the Platte River Basin's (PRB) seasonal changes in climate in a given year can be unpredictable and severe. Land areas in the PRB are devoted to natural cropland and grassland ecosystems, making it a region where untouched and cultivated systems coexist. Projected increments of the recurrence of hydrometeorological extreme events coupled with inefficient water use in agriculture challenge the sustainability of the fourth largest irrigated area in the nation and one of the last prairie ecosystems in North America. Considering groundwater a finite resource, the PRB's soil moisture may represent a “seasonal” storage and source of water that contributes to maintain crop and ecosystem functions under harsh weather conditions. However, the effect of drought and flood events on evapotranspiration (ET), soil moisture (SM), and their association is poorly understood. This gap in our knowledge raises the following scientific question: How do soil moisture and evapotranspiration respond to extreme wet and dry conditions, and how can they improve the predictability of future land surface hydrology in the region? Our hypothesis is that land-use changes in response to climate forcing and human activities, monitored through variations in their SM and ET, will be more resilient after flood than drought events. The hypothesis will be tested by achieving a better understanding of historical and current water states in the Platte River Basin, one of the key components of predictability. With the use of the Variable Infiltration Capacity (VIC) model and remote sensed land use changes, we simulate land surface hydrology variables and state variables. VIC's forcings are precipitation, minimum and maximum temperatures, and wind speed (obtained from the Sub-continental Observation Dataset, a gridded 1/16th degree resolution data obtained from climatological stations in Canada, US, and Mexico). VIC integrates physical properties at the land surface in soil, snow, and vegetation files. In the vegetation file, a fixed seasonal Leaf Area Index (LAI) is used to identify the statistical properties of extreme events simulated by VIC from 1950-2013. Then, the vegetation-file is substituted by an 8-day LAI obtained from MODIS to evaluate ecosystem and agro-ecosystem resiliency from 2001-2013 (overlapping years of forcing and remote sensed LAI). The PRB will be divided into its major sub-basins (Elkhorn, Loup, North Platte, South Platte) in order to examine climatological differences. Preliminary results show a slow recovery of soil moisture to multi-month drought events estimated from a gamma distribution function.