资源环境科技发展态势分析平台

Warm-season rainfall characteristics in the central United States are investigated as they play important roles in ecohydrology and agricultural productivity. Using rainfall observations, we compare the April-August mesoscale convective systems (MCS) and non-MCS rainfall characteristics and examine their linear trends between 1997 and 2018. MCS rainfall is found to be approximately seven times more intense than non-MCS rainfall but it occurs less frequently in time and space. MCS rainfall peaks in nocturnal hours, with synchronized timing of rainfall intensity, area, and occurrence, while non-MCS rainfall peaks in late-afternoon hours, mostly attributed to the timing of peak rainfall area. MCS rainfall has increased in the last 22 years due to an increase in frequency and a longer duration per MCS. In contrast, non-MCS rainfall has decreased mainly due to a reduction in rainfall area, leading to fewer total wet days and increased dry intervals between events.

Plain Language Summary Frequent light-to-moderate rainfall can benefit vegetation while infrequent but heavy rainfall may produce floods. Such differences in rainfall intensity and frequency between mesoscale convective systems (MCSs), a form of organized deep convection, and other warm season rainfall in the central United States are not well understood, despite the importance to local responses of ecohydrologic systems. This study aims to quantify the differences of MCS and non-MCS rainfall characteristics and investigate their changes in the recent decades. We found that MCS-contributed rainfall is approximately seven times more intense than non-MCS rainfall, but it occurs less frequently in time and space. More importantly, we found that MCS rainfall has been increasing recently due to an increased frequency of MCS events sweeping the central United States and a longer duration per MCS storm. However, non-MCS rainfall has been decreasing because of decreased rainfall area. Such increases of heavy rainfall at the expense of more moderate rainfall leads to decreasing wet days and longer dry periods between storms, which may increase the risk of flooding and significantly impact drought prone ecosystems.