Unveiling Trends in Hydroclimate Extremes using High-spatiotemporal Resolution Climate Data Records of Precipitation
Precipitation is a vital component of the water-energy-food nexus and a deadly force of nature responsible for natural hazards like flooding and debris flows. Because of its profound impact to society at large, it is an extremely important variable to measure and predict. Fittingly, the highly variable and chaotic nature of the precipitation field makes quantifying and forecasting arduous. One tool useful for precipitation measurements are satellites, which are capable of measuring precipitation quasi-globally over land and oceans. Given the rapid advancement of remotely sensed observational techniques over the past few decades and the satellite record’s recent emergence into climate time scales, new kilometer-scale, sub-daily records of precipitation have been produced capable of high-spatiotemporal insights into some of the most extreme hydroclimate events. With climate change’s influence becoming more profound through the passage of time, this dissertation seeks to examine how atmospheric rivers (ARs) and tropical cyclones (TCs) have evolved since the beginning of the satellite age using high resolution climate data records of precipitation (HRPCDRs) and testing for the influence of anthropogenic warming. In the first half of the dissertation, we adapt the CONNected-objECT (CONNECT) algorithm for the tracking of global mid-latitude AR lifecycles and associated precipitation by implementing a seeded region growing segmentation algorithm, creating the AR-CONNECT algorithm. One of AR-CONNECT’s goals is to track atmospheric water vapor anomalies before evolving into AR geometries, effectively tracking AR genesis farther back than other studies. To accomplish this, AR-CONNECT is without hard-coded geometric criteria yet is still proven to extract synoptic-scale elongated objects >99.99% of the time. With the aid of sub-daily satellite-derived rain data, we investigate the climatology, trends, and patterns of AR lifecycles from 1983-2016 and compare with other AR tracking studies. We find that AR frequency, genesis, and terminus locations are in generally good agreement with other AR tracking methodologies and that AR frequencies in each hemisphere are proportional to the number of AR hotspots. In terms of precipitation, mid-latitude precipitation uncovered by AR-CONNECT shows contributions up to 50% over land and 65% over the ocean. We show that annual values of total rainfall volume, mean size, and mean duration of ARs have increased, conceivably because of greater atmospheric water vapor concentrations from anthropogenic warming. Spatial trend analysis of AR precipitation show increase in precipitation associated with Southern Hemisphere and northern African ARs, among others, but is determined not to be a driver of changes in global precipitation. In the latter half of the dissertation, we investigate precipitation trends in global TCs. Increases in precipitation rates and volumes from TCs caused by anthropogenic warming are predicted by climate modeling studies and have been identified in several high intensity storms occurring over the last half decade. However, it has been difficult to detect historical trends in TC precipitation at time scales long enough to overcome natural climate variability because of limitations in existing precipitation observations. We introduce an experimental global high-resolution climate data record of precipitation produced using infrared satellite imagery and corrected at the monthly scale by a gauge-derived product that shows generally good performance during two hurricane case studies but estimates higher mean precipitation rates in the tropics than the evaluation datasets. General increases in mean and extreme rainfall rates during the study period of 1980-2019 are identified, culminating in a 12-18%/40-year increase in global rainfall rates. Overall, all basins have experienced intensification in precipitation rates. Increases in rainfall rates have boosted the mean precipitation volume of global TCs by 7-15%/year, with the starkest rises seen in the North Atlantic, South Indian, and South Pacific basins (maximum 59-64% over 40 years). In terms of inland rainfall totals, year-by-year trends are generally positive due to increasing TC frequency, slower decay over land, and more intense rainfall, with an alarming increase of 81-85% seen from the strongest global TCs. As the global trend in precipitation rates follows expectations from warming sea surface temperatures (11.1%/°C), we hypothesize that the observed trends could be a result of anthropogenic warming creating greater concentrations of water vapor in the atmosphere, though retrospective studies of TC dynamics over the period are needed to confirm.