The Contribution of Mesoscale Convective Systems to Intense Hourly Precipitation Events during the Warm Seasons over Central East China

Central East China is an area where both intense hourly precipitation（IHP） events and mesoscale convection systems（MCSs） occur frequently in the warm seasons. Based on mosaics of composite Doppler radar reflectivity and hourly precipitation data during the warm seasons（May to September） from 1 July 2007 to 30 June 2011, the contribution of MCSs to IHP events exceeding 20 mm h^-1 over central East China was evaluated. An MCS was defined as a continuous or quasicontinuous band of 40d BZ reflectivity that extended for at least 100 km in at least one direction and lasted for at least 3h. It was found that the contribution of MCSs to IHP events was 45% on average over central East China. The largest contribution,more than 80%, was observed along the lower reaches of the Yellow River and in the Yangtze River–Huaihe River valleys.These regions were the source regions of MCSs, or along the frequent tracks of MCSs. There were two daily peaks in the numbers of IHP events： one in the late afternoon and one in the early morning. These peaks were more pronounced in July than in other months. MCSs contributed more to the early-morning IHP event peaks than to the late-afternoon peaks. The contributions of MCSs to IHP events with different intensities exhibited no significant difference, which fluctuated around 50% on average over central East China.

On the Increased Precipitation Recycling by Large-Scale Irrigation over the Haihe Plain

Irrigation not only plays an important role in global food security,but it also affects aspects of the regional climate,including precipitation.In this study,we proposed a simple and convenient method to quantify the contribution of large-scale irrigation to precipitation by distinguishing the amount of evaporation generated by irrigation from local evaporation based on the precipitation recycling method.A case study was presented to show the increased precipitation recycling ratio and the contribution of irrigation to precipitation during the main irrigation period in the Haihe Plain from 1961 to 2016.We found that the average precipitation recycling rates in the Haihe Plain are 8.32%,9.74%,and 10.36%in April,May,and June,respectively.The contribution rates of irrigation to precipitation in the Haihe Plain are 3.76%,5.12%,and 2.29%in April,May,and June,respectively.The total contribution of irrigation to precipitation during the main irrigation period is 3.77 mm;the respective contributions in April,May,and June are 0.72,1.70,and 1.35 mm.The contribution of irrigation to local precipitation is relatively small as the inflow of atmospheric moisture during the irrigation period is still the main factor affecting local precipitation.Nevertheless,this part of the precipitation during the irrigation period alleviates the water shortage in the Haihe Plain to some extent.