Scope effects in contingent valuation: an application to the valuation of irrigation water quality improvements in Infulene Valley, Mozambique
Date
2018-02
Authors
Graça, Manjate
Journal Title
Journal ISSN
Volume Title
Publisher
African Economic Research Consortium
Abstract
This study uses the double-bounded bid elicitation format to test whether the willingness to
pay (WTP) of 244 randomly selected residents of Maputo and Matola cities for wastewater
quality improvements in the Infulene Valley is sensitive to internal and external scope. The
Infulene Valley was selected because its wastewater is used as an input in vegetable irrigation.
WTP was elicited and compared when the level of wastewater treatment was 100 % and when
it was 50 %. The results show that the majority of those interviewed display high levels of
knowledge regarding the risks associated with poor quality irrigation water, and that they have
attitudes and perceptions receptive to a policy that aims to improve irrigation water quality.
The WTP responses passed the bottom up (t= 15.28, p=0.000) and top down (t=14.07, p=0.000)
internal and external (t=13.43, p=0.000) scope tests, suggesting that the level of wastewater
treatment significantly influences households’ WTP. The following variables were statistically
significant in the WTP model: income, age, education level, household size, gender, whether
the household considers water scarcity as a priority issue, knowledge of the unsuitability of
Infulene Valley water for vegetable irrigation, and whether the household is aware that the
Infulene Valley is an important supplier of fresh vegetables to Maputo and Matola residents.
The study concluded that the level of water treatment (high quality of treated wastewater) is a
significant factor of preference over the alternative policy in wastewater treatment. The
following recommendations derive from the study: policy makers should consider wastewater
treatment planning and they should develop an irrigation water pricing system, as well as
conservation practices to manage pollution problems at Infulene Valley. While this study
provides an estimate of household values for irrigation water quality improvements in the
Infulene Valley, is ultimately up to policy makers at the city and country levels to implement
any changes.
Description
Keywords
Recycled wastewater reuse, irrigation, willingness to pay, scope effects in contingent valuation, double- bound dichotomous choice bid elicitation format, Mozambique