HYDROLOGICAL RESPONSE OF LAKES ON KIRITIMATI ISLAND, KIRIBATI TO RECENT CLIMATE VARIABILITY

Kiritimati Island, Republic of Kiribati, located in the central tropical Pacific (CTP) contains hundreds of shallow lakes that potentially archive past and regional moisture balance, but the response of island hydrology to regional climate variability remains poorly constrained due to lack of continuous measurements of precipitation, evaporation, and temperature. Chemistry surveys and physical observations of select lakes indicate the recharge sources are various and complex, with some connected to the main lagoon and influenced by the tide, some influenced mostly by precipitation and evaporation, while others are controlled by lower-frequency fluctuations in groundwater. Understanding how the numerous lakes reflect the regional climate is important considering local hydroclimatic data scarcity in the face of a warming climate and projected sea level rise for Kiribati amidst a growing population dependent on these lakes for their livelihoods. In this study, Landsat images are used to calculate the ratio of total water area to total land area (W/L) for the entire island and for three smaller regions. W/L for the entire island is positively correlated with local precipitation and negatively correlated with regional evaporation, indicating that the lakes grow in area in response to precipitation and shrink in response to evaporation. Over a 12-month period, the highest correlation for the island occurs at a 3-month lag, but a comparison with three isolated regions indicates brackish groundwater-fed lakes (A) have a 2-month lag with precipitation, suggesting that hydrologic memory is unique to different regions of the island. The hypersaline lakes adjacent to the main lagoon (B), and isolated lakes in the remote southeastern end of the island (C) also have a negative correlation with evaporation, but the response is decoupled from region A. A comparison of W/L to NINO 3.4, a key El Niño/Southern Oscillation (ENSO) metric that reflects regional sea surface temperature shows that region C is most highly correlated with the index. The results suggest strong links between surface hydrology on Kiritimati and the influence of ENSO on regional moisture balance. However isolating regions of the island shows the hydrologic response is variable based on lake type and time scale.