The midsummer drought in Mexico: perspectives on duration and intensity from the CHIRPS precipitation database

In many regions of Mexico, precipitation occurs in a very well defined annual cycle, with peaks in May-June and September-October and a relative minimum in the middle. This minimum in the middle of the rainy season is known as the midsummer drought (MSD) and impacts agriculture and industry. However, in Mexico there are large areas with either sparse meteorological station coverage or where time series of historical observations have many missing data, which make it difficult to study and analyse the precipitation variability at different scales of space and time. Therefore, the most important objective of this study is to evaluate the performance of the recently available Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) product in estimating the duration and intensity of the MSD in Mexico, taking advantage of its very fine spatial resolution (0.05 degrees) and continuous coverage to improve on current understanding of the MSD. In order to achieve this, MSD duration and intensity are calculated from the CHIRPS data and then compared to gauge data for the 1981-2010 period. In addition, two new indices for estimating the intensity of the MSD are defined, and these new indices provide complementary information to that obtained with more traditional methods. Results show that CHIRPS overestimates (underestimates) precipitation in Mexico during summer and autumn (winter and spring) seasons by up to 30%. Most importantly, by using CHIRPS and the two new indices proposed, the most detailed spatial representation ever of the MSD in Mexico has been obtained through the elimination of spatial and temporal coverage gaps.