Understanding Rainfall Variability and Its Impact on Precipitation Effectiveness
Most regions of the United States have experienced an increasing trend in heavy precipitation and precipitation intensity, defined as the amount of precipitation falling over a given period . The impact of increasing rainfall intensity on drought, and soil moisture particularly, is complex and not well understood. Negating the influence of evapotranspiration, more rainfall over a given period should lead to an increase in terrestrial water storage. However, soil infiltration rates limit water storage under particularly intense rainfall, potentially resulting in less soil water storage with increasing rainfall intensity (Liu et al. 2011; Cuomo and Dealla Sala 2013; Ren et al. 2020).
Practically, the same amount of rain falling over an area could potentially net less soil water storage if the rainfall is more intense (i.e., falling over a shorter time), with more rainfall partitioned to runoff. This hydrologic response to climate change and increasing precipitation intensity has been the focus of much research, with inconsistent results that are largely sensitive to the methods by which each component of the land surface hydrologic cycle is represented.
The response of soil moisture to trends in precipitation variability and intensity is critical for understanding potential changes in drought and flooding events and mitigation of associated impacts. Increasingly intense rainfall across the U.S. has the potential to reduce drought monitoring efficacy of many frequently-used indices that do not directly incorporate soil moisture information. This project seeks to improve our understanding of soil moisture response to increasingly intense precipitation, using a combined observation-physical modeling approach. This research directly addresses new challenges for drought assessment, which were outlined in the NIDIS publication Drought Assessment in a Changing Climate: Priority Actions & Research Needs.
This project will be accomplished through two primary objectives:
- Assess soil moisture response to changes in precipitation intensity using both a process-based hydrological model (Soil and Water Assessment Tool or similar) and observation-based assessment of soil moisture relationships using observations from the Illinois Climate Network.
- Evaluate the ability of commonly-used drought indices such as Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) to represent soil moisture under varying precipitation intensity.
For more information, please contact Molly Woloszyn (molly.woloszyn@noaa.gov).
Research Snapshot
Dr. Trent Ford, Illinois State Water Survey, Prairie Research Institute, University of Illinois Urbana-Champaign
Zhenxing Zhang and Momcilo Markus, Illinois State Water Survey, Prairie Research Institute, University of Illinois Urbana-Champaign
What to expect from this research
- Journal publications on the hydrological model and observational analysis.
- Communication piece(s) (e.g., webinar, news story, or 2-pager) that will highlight key project findings and takeaways.
- A white paper that will use the project findings to remark on the state of drought monitoring in the U.S., especially as it relates to the strengths and weaknesses of incorporating heavy precipitation events and large seasonal variability.
