A View from the Top: Satellite-Observed Changes to the Water Cycle

Satellite estimates of precipitation rates are less direct than those from rain gauges, but offer the advantage of a global view. Microwave radiometers, like those on the SSM/I and SSMIS, provide a continuous view of the rain rates over the global oceans since 1987. Significant efforts have been recently focused on developing and maintaining a continuous intercalibrated data record of some geophysical parameters observed by these and other MW radiometers. As a result of these efforts, Remote Sensing Systems recently released the MW geophysical ocean products Version 7, a 25-yr climate-quality record of total columnar water vapor, rain rates, cloud liquid water, and surface winds. Analyses of 20-years of data from the previous version (V6) highlighted a major discrepancy between the rate of change of global precipitation and evaporation from satellite estimates compared to that predicted by climate models (Wentz et al, 2007). Those results stimulated a significant debate in the scientific community, still ongoing. Here we look at current satellite estimates of changes to the water cycle extended to 2013, and discuss the uncertainty in these estimates. However, global observed trends tend to be very small and estimating them with high accuracy is challenging. Therefore, rather than on global trends, here we will focus on the regional patterns of change in precipitation and in the other geophysical parameters, which present strong statistically-significant signals. What are the spatial patterns of observed changes in precipitation, water vapor, and surface winds? Are observed changes in the atmospheric circulation and in the water cycle consistent with each other? How can they be explained? Are current climate models (CMIP5) able to reproduce these patterns, and the consistency among the different observed variables?