| Dengue fever impacts populations across the tropics, and its burden is projected to increase under future scenarios. The transmission process of dengue virus is strongly moderated by hydro-climatic conditions that impact the vector's life cycle and behavior. We study the impact of rainfall seasonality and moisture availability on the monthly distribution of reported dengue cases in Sri Lanka. We find an association between seasonal peaks of rainfall and dengue incidence with a two-month lag through cluster analysis. We show that a hydrologically driven epidemiological model (HYSIR), which takes into account hydrologic memory in addition to the nonlinear dynamics of the transmission process, captures the two-month lag between rainfall and dengue cases seasonal peaks. Our analysis reveals a non-monotonic dependence of dengue transmission rate on moisture, whereby an increase of transmission rate with increasing moisture is followed by a reduction for very high levels of water availability. Improvement in prediction of the seasonal peaks in dengue incidence results from a seasonally varying dependence of transmission rate on water availability. |