Quantification of an overlooked water resource in the tropical rainfed lowlands using RapidEye satellite data: A case of farm ponds and the potential gross value for smallholder production in southern Laos

In southern Laos, water stored in farm ponds is largely underutilised as it is perceived to be unfit for human consumption; subsequently, groundwater is the preferred source for domestic and agricultural consumption. For the first time, this paper presents the results of a study designed to quantify the total pond water volume within the landscape via remote-sensing methods in two districts in Champasak province that could be used to improve rural household cash income through the expansion of market-oriented dry season crop production. Water bodies were delineated via simple classification of RapidEye data using the Normalised Difference Water Index and a sub-classification was performed to distinguish between ponds and the streamflow network. Final estimates of total pond volume in Sukhuma and Phonthong districts were ∼2.30 × 106  m3 and 3.55 × 106 m3, respectively; and the average pond volume across both districts was ∼1987 m3. Sensitivity analysis of the potential gross value of farm ponds for irrigation of dry season, vegetable production typical of market-oriented smallholder activities in the area indicated that substantial gross economic gains could be made from better use and management of these resources.