In our new study (led by PhD student Imme Benedict), we have assessed the water budget of the Mississippi River Basin under present and future climate conditions. Our main aim was to find out where the precipitation originates from, and in particular whether this comes from land or ocean. To find this out, we apply moisture tracking to climate model output data from simulations that represent the current situation as well as simulations for a future climate based on the RCP4.5 scenario.
For the present climate, the most important continental moisture sources are the Mississippi River Basin itself and the area southwest of the basin. The two most relevant oceanic sources are the Gulf of Mexico/Caribbean and the Pacific. The distribution of sources varies per season, with more recycling of moisture (rainfall generated by local evapotranspiration) within the basin during summer and more transport of moisture from the ocean toward the basin in winter. In future winters, we find an increase in moisture source from the oceans, related to higher sea surface temperatures due to global warming. This results in more precipitation over the Mississippi River Basin. In future summers, the basin itself contributes 5% less to the precipitation (i.e., less recycling). Overall, we conclude that Mississippi’s moisture sources will become less local in a future climate, with more water originating from the oceans.
Benedict, I., van Heerwaarden, C.C., van der Ent, R.J., Weerts, A.H., and Hazeleger, W., 2020. Decline in terrestrial moisture sources of the Mississippi river basin in a future climate. Journal of Hydrometeorology, https://doi.org/10.1175/JHM-D-19-0094.1.