Introducing a Network of Experimental Catchments in the Urban Tropics

This contribution introduces three tropical experimental catchments across diverse urban settings in Singapore, designed to advance understanding of runoff generation across different land-uses. Rapid urbanization in tropical cities magnifies hydrological complexity, yet the processes governing runoff formation remain poorly quantified, especially at finer spatial scales. Tropical rainfall events are highly variable in space and time, and runoff formation processes, including interactions between surface and subsurface flow, typically exhibit pronounced heterogeneity due to the complexity of urban structures and diverse soil characteristics.

Here we introduce a new experimental catchment network, comprising three primary catchments, each spanning a few hectares in size. Catchments are densely instrumented for high resolution monitoring of hydrological and ecological processes, including rain gauges and meteorological stations, lysimeters, pressure transducers in wells and channels, leaf wetness sensors, rain gutter for throughfall measurement, sapflow meters and dendrometers, soil moisture sensors and water potential probes. This diverse instrumentation enables high-resolution data collection on precipitation, infiltration, discharge dynamics as well as vegetation ecophysiology.

The three experimental catchments, i.e. Kent Ridge catchment, Gallop catchment located within the Singapore Botanic Gardens, and Everton/Blair catchment near Duxton Hill vary greatly in their land-cover composition. Kent Ridge represents catchment with a mixed land-use, combining urbanized areas, parks, and remnants of tropical secondary forest. It is characterized by a higher proportion of built-up areas and an extensive system of open artificial drainage canals. In contrast, Gallop catchment is dominated by pervious natural surfaces, represented by tropical vegetation (rainforest, managed trees and lawns). Everton/Blair catchment contains highly sealed surfaces with low-rise buildings and occasional trees, open drainage canals and relatively flat terrain within Singapore’s central urban district.

Preliminary data illustrate differences in both surface and subsurface hydrological responses across these catchments, highlighting the influence of land-use, soil properties, and urban infrastructure on water storage and flow pathways. The collected high-resolution data aim to improve mechanistic understanding and modelling of hydrological responses in rapidly urbanizing tropical environments.