Base flow-driven shifts in tropical stream temperature regimes across a mean annual rainfall gradient

Abstract

Climate change is expected to affect air temperature and watershed hydrology, but the degree to which these concurrent changes affect stream temperature is not well documented in the tropics. How stream temperature varies over time under changing hydrologic conditions is difficult to isolate from seasonal changes in air temperature. Groundwater and bank storage contributions to stream flow (i.e., base flow) buffer water temperatures against seasonal and daily fluctuations in solar radiation and air temperature while rainfall-driven runoff produces flooding events which also influence stream temperature. We used a space-for-time substitution to examine how shifts in base flow and runoff alter thermal regimes in streams by analyzing hydrological and temperature data collected from similar elevations (400-510 m above sea level) across a 3500 mm mean annual rainfall gradient on Hawai‘i Island. Sub-daily water temperature and streamflow gathered for three years were analyzed for daily, monthly, and seasonal trends and compared to air temperature measured at multiple elevations. Results indicate that decreases in median base flow increased mean, maximum and minimum water temperatures as well as daily temperature range. Monthly and daily trends in stream temperature among watersheds were more pronounced than air temperature, driven by differences in groundwater inputs and runoff. Stream temperature was strongly negatively correlated to base flow during the dry season but not during the wet season due to frequent wet season runoff events contributing to total flow. In addition to projected increases in global air temperature, climate driven shifts in rainfall and runoff are likely to affect stream flow and groundwater recharge, with concurrent influences on base flow resulting in shifts in water temperature that are likely to affect aquatic ecosystems.

Citation

Strauch, Ayron M.; MacKenzie, Richard A.; Tingley, Ralph W. 2017. Base flow-driven shifts in tropical stream temperature regimes across a mean annual rainfall gradient. Hydrological Processes. 31(9): 1678-1689. https://doi.org/10.1002/hyp.11084.