Assessing Mountain Soil Water Storage and Release in a Colombian Páramo With APSIS-InSAR Data

Direct observation of montane and upland water resources provides valuable data in support of national scale water management and policy, but direct observation is challenging on large spatial scales. To address the need for large spatial scale hydrological data we use InSAR surface motion signals, indicative of surface swelling due to increased soil water content, at approximately 90 m resolution over a tropical Colombian mountain range covered with Páramo, a biome widespread along the Northern Andes. Considering uncertainty of vegetation and mountainous terrain on the InSAR signal, we observe a regional, spatially consistent sequence of soil surface motion, which can be related to storage and movement of water through montane catchments. Swelling on the ridges and upper slopes occurs during the wet season and is consistent with infiltration and increased saturation of ridge and upper slope soils. This is followed by a marked swelling of the valley floors towards the end of the wet season and into the dry season. The InSAR signal also captures movement of water through the basin with swelling subsiding sequentially downslope and downstream. The results indicate that a shallow hillslope flow dominates during the wet season, but this alone is insufficient to explain shallow ground water storage in superficial valley deposits lasting into the late wet season and dry season. We conclude that InSAR signals can provide a qualitative insight in the storage and release mechanisms at a basin scale, thus complementing sparse point-scale measurements.