Constraining Regional Hydrological Sensitivity Over Tropical Oceans

• Published in: Geophysical research letters 2024-09, Vol.51 (18), p.n/a
• Main Authors: He, Jie, Deng, Yi, Fosu, Boniface, Lin, Yen‐Heng, Lu, Kezhou
• Format: Article
• Language: English
• Subjects: Atmospheric circulation; Climate and weather; Climate change; Climate models; Convergence; Future precipitation; Global climate; global warming; Hydrologic models; hydrological sensitivity; Hydrology; Ocean models; Oceans; Precipitation; Sea surface temperature; Sensitivity; Surface temperature; Surface wind; Temperature gradients; tropical precipitation; Uncertainty; Weather patterns; Winds
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL109374

Regional hydrological sensitivity (i.e., precipitation change per degree local surface warming) contributes substantially to the uncertainty in future precipitation projections over tropical oceans. Here, we investigate the sensitivity of relative precipitation (P*, precipitation divided by the basin average precipitation) to local sea surface temperature (SST) change by dissecting it into three components, namely the sensitivity of P* to relative SST (SSTrel, SST minus the tropical mean SST) changes, the sensitivity of P* to surface convergence changes, and the sensitivity of surface convergence to SST gradient changes. We show that the relationships between P* and SSTrel, and between P*, surface convergence, and SST gradients are largely constant during climate change. This allows us to constrain regional hydrological sensitivity based on present‐day SST‐precipitation relationships. The sensitivity of surface convergence to SST gradient changes is a main source of uncertainty in regional hydrological sensitivity and is likely underestimated in GCMs. Plain Language Summary Understanding how precipitation will change over tropical oceans is important because these changes influence the atmospheric circulation, which in turn affects the global climate and weather patterns. Climate models disagree on their projections of precipitation changes over tropical oceans in part due to a lack of understanding on how precipitation should respond to a given amount of local surface warming. We find that the sensitivity of precipitation to future changes in local sea surface temperature (which is commonly referred to as regional hydrological sensitivity) largely depends on the present‐day relationship between precipitation and local sea surface temperature, as well as that between precipitation and the spatial gradient in sea surface temperature, and both relationships are observable and thus can serve as constraints. We find that inter‐model differences in regional hydrological sensitivity result primarily from differences in the response of surface winds to sea surface temperature gradient changes. Key Points Regional hydrological sensitivity is an important source of uncertainty in rainfall projections over tropical oceans Regional hydrological sensitivity can be constrained by components of rainfall‐temperature relationship that stay constant during warming Uncertainty in regional hydrological sensitivity originates largely from surface convergence sensitivity to te