The summer-time American Monsoon region experiences large variations in precipitation, leading to significant impacts on hydrology. These fluctuations are poorly represented in climate models, making it challenging for predicting future changes and enforcing countermeasures. The project analyzed ... Show moreThe summer-time American Monsoon region experiences large variations in precipitation, leading to significant impacts on hydrology. These fluctuations are poorly represented in climate models, making it challenging for predicting future changes and enforcing countermeasures. The project analyzed the National Center for Atmospheric Research (NCAR)'s Community Earth System Model 1 (CESM1) Large-Ensemble to determine how robust and reliable the model is at predicting the monsoon on seasonal and daily timescales. It examined the precipitation over the US, focusing on the Southwest summer-time monsoon, how it is simulated and how it might change in the future. Examination of pre-industrial, present day and future CESM1 simulations revealed that the monsoon simulation is somewhat deficient compared to observations. Rather than a localized maximum centered over the Arizona and New Mexico regions, there is a westward extension of the spurious north-south elongated precipitation feature positioned along the Eastern Rocky Mountains. Furthermore, the seasonality of the monsoon exhibited a shift of about a month, with the onset moving closer to August and significant rains still seen in September. These simulation shortcomings could call into question the reliability of future projections. The dominant climate change simulated showed an increase in monsoon rainfall and humidity, consistent with the inevitable surface temperature rise. The location of these increases are, however, distant from the observed and are co-located with the model’s main precipitation bias. An analysis of the daily precipitation PDF revealed that the model does not predict a significant change in extreme events and reflected the same regional biases. Show less
