MODELING REGIONAL WEATHER PATTERNS IN SOUTHERN ILLINOIS BY INTEGRATING STABLE WATER ISOTOPES FOUND IN PRECIPITATION TO DISTINGUISH VARIOUS CONTROLS ON THE LOCAL HYDROLOGIC CYCLE

This study pertains to better understanding the water cycle in Southern Illinois, and by extension, the Midwestern United States, by quantifying the temporal variations in the contribution of different moisture sources (i.e., evaporated ocean water and local moisture recycled through evapotranspiration) to local precipitation. A better understanding of the water cycle dynamics is needed for predicting extreme weather events such as droughts and floods as well as assessing the sensitivity of regional hydrologic and bioecological systems to climate variations.

Here we report stable isotope values (δ¹⁸O and δD) of individual precipitation events collected from November 2012 to February 2016 in Carbondale, Illinois. The isotope data was integrated with climate parameters as well as HYSPLIT modeling. The HYSPLIT was used at altitudes of 300, 500 and 850 meters above ground level to ascertain backwards trajectories of individual precipitation events. We identified five distant advective moisture sources, namely: (a) the Pacific Ocean, (b) the Arctic Jet Stream and the upper continent of the Northern Rockies and Plains, (c) the lower continent in the South and Southwest, (d) the Gulf of Mexico, and (e) the Atlantic Ocean. Convective moisture sources are regarded as occurring locally, which in this study is defined geographically as the area extending from 35.00° N to 45.00° N and -87.00° W to -95.00° W

Our results show that, the local meteoric water line (MWL) has a slope of 7.6 and an intercept of 10.5, values similar to those of the global MWL. Precipitation isotopic and deuterium excess (d-excess) values show clear seasonality. The d-excess parameter can be taken as a measure of the contribution of recycled water to precipitation. Additionally, our results show that the two major components to local precipitation were the moisture originating from local recycled water through evapotranspiration and the moisture originated from the Gulf of Mexico.

In the Midwestern portion of the United States most of the surface water is stored in soil and vegetation, changes in the amount as well as transfer rates among these reservoirs can have a significant effect on the regional land-atmosphere water fluxes with direct implications on economic activities.