Observed and Projected Precipitation Changes over the Nine US Climate Regions

Abstract

Abstract:We analyze the past temperature and precipitation changes in nine separate US climate regions. We find that the temperature increased in a statistically significant (95% confidence level equivalent to alpha level of 0.05) manner in all of these regions. However, the variability in the observed precipitation was much more complex. In the eastern US (east of Rocky Mountains), the precipitation increased in all five climate regions and the increase was statistically significant in three of them. In contract, in the western US, the precipitation increased in two regions and decreased in two with no statistical significance in any region. The CMIP5 climate models (an ensemble mean) were not able to capture properly either the large precipitation differences between the eastern and the western US, or the changes of precipitation between 1900 and 2015 in eastern US. The statistical regression model explains the differences between the eastern and western US precipitation as results of different significant predictors. The anthropogenic greenhouse gases and aerosol (GHGA) are the major forcing of the precipitation in the eastern part of US, while the Pacific Decadal Oscillation (PDO) has the major influence on precipitation in the western part of the US. Our analysis suggests that the precipitation over the eastern US increased at an approximate rate of 6.7%/K, in agreement with the Clausius-Clapeyron equation, while the precipitation of the western US was approximately constant, independent of the temperature. Future precipitation over the western part of the US will depend on the behavior of the PDO, and how it (PDO) may be affected by future warming. Low hydrological sensitivity (percent increase of precipitation per one K of warming) projected by the CMIP5 models for the eastern US suggests either an underestimate of future precipitation or an overestimate of future warming.

Response of Natural Vegetation to Climate in Dryland Ecosystems: A Comparative Study between Xinjiang and Arizona

“…In general, Arizona was dominated by warming trends with insignificant changes in daily precipitation anomalies during the past two decades. Despite the paucity of (historical) climate change studies focusing exclusively on the entire Arizona, the observed patterns are found in generally good agreement with many regional studies [53][54][55][56]. For example, Garfin et al [54] pointed out that there was only little change in mean annual precipitation from 1901 to 2010; this was later confirmed by Chylek et al [53], in which no statistically significant trend was observed in the western part of the U.S.…”

“…Remote Sens. 2020, 12, x FOR PEER REVIEW 11 of 26 confirmed by Chylek et al [53], in which no statistically significant trend was observed in the western part of the U.S.…”

Intercomparison of the Surface Energy Partitioning in CMIP5 Simulations

“…During the 20th century, intensification of the global hydrological cycle has been observed [1], and the trend is expected to continue under a warming climate [2]. The established robust responses of the global hydrological cycle to temperature rise include amplified variance of precipitation everywhere [3], increased precipitation intensity over land [4,5], land evapotranspiration acceleration [6], and reduced soil moisture [7]. The long-term decline in soil moisture is the only response that has not been validated against in-situ measurements, as historical ground observations are limited [8] and soil moisture products derived from satellites are sensitive to the accuracy of retrieval algorithms [9,10].…”