CHANGING PRECIPITATION PATTERNS IN THE U.S. MIDWEST: CAUSES AND CONSEQUENCES

There is growing evidence that human-induced climate change is changing global patterns of precipitation and the hydrological cycle. Over the past twenty years, numerous studies have detected remote associations (teleconnections) between rising air temperatures and global precipitation, since a warmer climate spurs the evaporation of water from land and sea and allows the atmosphere to hold more moisture. As a result, wet places tend to get wetter and, similarly, dry places tend to get drier, increasing the risks of extreme weather events such as floods and droughts. The U.S. Midwest has experienced noticeable changes in its climate over the last several decades. From 1900-1950, temperatures have increased at a rate of 0.06 °C/decade, but over the last 50 years this rate has jumped to 0.26 °C/decade. Heat waves are becoming more frequent and cold periods are becoming rarer. Precipitation patterns have also changed, and the last three decades have been the wettest on record. Heavy downpours now occur twice as frequently as they did a century ago. Summer rainfall currently accounts for almost 50% of the annual total, and most of this precipitation results from small scale, regional systems. Snow and ice are arriving later in the fall and starting to melt earlier in the spring. Significant spatial and temporal variabilities have been observed throughout the region, and are described in this presentation. In addition, we explore possible causes for these trends in precipitation – including the teleconnections with oceanic-atmospheric events such as ENSO, AMO and PDO – and the multiple consequences for resource management, emergency preparedness, and water availability for irrigation and domestic use.