# Satellite Remote Sensing of Precipitation and the Terrestrial Water Cycle in a Changing Climate
## 3 Satellite Measurement of Precipitation
### Scientific and Technological Challenges
#### 3.2.6. Observing Extremes  
An important discussion concerns the capability of satellite precipitation products to capture extremes and their climatological cycles. Despite uncertainties in total precipitation changes, observations and climate models show robust increases in extreme daily precipitation averaged over both dry and wet regimes over the past six decades; climate projections for the rest of the century point to continued intensification of daily precipitation extremes [228] and the same indicate observations [229]. The CC scaling on temperature may turn out to provide a severe underestimate of observed changes in hourly rainfall extremes, with implications for assessing the impacts of extreme rainfall [230]. It also found that human-induced climate change likely increases the chances of the observed precipitation accumulations during hurricane landfall [231]. This induces wet and dry hydrological extremes, and a quantification of their global cooccurrence is crucial for disaster preparedness [232]. A specific study by Prat and Nelson [233] on the link between tropical cyclones (TC) and daily rainfall extremes using satellite observations has concluded that TCs account for an average of \(3.5\%\pm 1\%\) of the total number of rainy days over land areas experiencing cyclonic activity, regardless of the basin considered. In spite of the general agreement on extremes, their relative weight and expected increase in the future due to higher available moisture content, we still do not fully understand the relationship between the mean state of precipitation and intense precipitation frequency on the most recent climate scale [234]. Studies need to investigate changes in intensity, frequency, and trends, and their links to large-scale features [235]. The advent of satellite global precipitation products extending to high latitudes and of sufficient temporal length has given rise to studies on the occurrence of extremes and their global distribution, yielding findings on model and observation weaknesses [236]. Houze et al. [237] show that extremely intense, deep, convective storms occur often during the warm season (April-September) in the high-latitude continents, where the increase of surface temperature has been greatest, indicating that high-latitude, extreme convection could be more common in a continually warming world. No single satellite precipitation product can be considered ideal for detecting extreme events. GPM IMERG is able to analyze extreme precipitation events (EPE) to derive their duration, areal coverage, total volume, and propagation [238]. AghaKouchak et al. [239] have demonstrated that all products tend to miss a significant volume of rainfall and to worsen their performance as the choice of extreme precipitation threshold increased. Resolution and accuracy limitations still persist in estimating extreme precipitation [240]. The definition of the accuracy in representing extreme rainfall events for varying time aggregation intervals is one more problem. A study of Mazzoglio et al. [241] concluded that satellite precipitation data guarantee good results when the rainfall aggregation interval is \(\geq\)12 h; a 24-h aggregation interval ensures a probability of detection \(>\)80%. At the same time, the results depend on the adopted spatial domain and require a multiscale approach to regional trend analysis [242]. Thus, more studies need to focus on capturing the fine time/space scale of extremes from satellite. The key problem is perhaps to disentangle the scale disparity between gridded and rain-gauge precipitation products and the short length of the available satellite records. In this direction, downscaling approaches appear to be a feasible avenue [243]. Satellite precipitation estimates are now contributing to our understanding of the role of major global moisture source regions in the occurrence of extreme monthly precipitation over the continents [244].