Climate, runoff and landuse trends in the Owo River Catchment in Nigeria

Abstract

Abstract. The Owo River is an important surface water source in Lagos particularly to the western section. It is the source of direct water intake for water supply by Lagos State Water Corporation to Amuwo-Odofin, Ojo and parts of Badagry Local Government Areas. This paper examines the complex interactions and feedbacks between many variables and processes within that catchment and analyses the future ability of this semi-urban watershed in sustaining water supply in the face of cumulative environmental change. Stationarity analysis on rainfall, change detection analysis and morphometry analysis were combined to analyse the non-stationarity of Owo River catchment. On rainfall trend analysis, since the correlation coefficient (0.38) with test statistic of 2.17 did not satisfy the test condition we concluded that there is trend and that rainfall in the watershed is not stationary. The dominant land use impacting on the bio-geochemical fluxes is built up area (including structures and paved surfaces) which grew from about 142.92 km 2 (12.20 %) in 1984 to 367.22 km 2 (31.36 %) in 2013 recording gain of 224.3 km 2 at average growth rate of 7.73 km 2 per annum. Total length of streams within the catchment reduced from 622.24 km in 1964 to 556 km in 2010, while stream density reduced from 0.53 in 1964 to 0.47 in 2010 an indication of shrinking hydrological network. The observed trends in both natural and anthropogenic processes indicated non-stationarity of the hydrological fluxes within the Catchment and if this continues, the urban ecosystem services of water supply will be compromised.

Human-Nature Interactions in the Owo River Catchment, South-West, Nigeria

“…Also, a high variability of rainfall characteristics (intensity, duration and frequency) is becoming more pronounced within the study area; a condition that is impacting seriously on raw water abstraction at Ishashi Intake [10] from the urban sub-catchments in Lagos. In addition to impacting on water availability, urbanization is also impacting on other hydrological responses of the catchments including runoff, peak flow and water quality, thereby, contributing to the non-stationarity or otherwise of the catchment [10]. However, a number of methods have been employed in studying human-environment interactions.…”

“…The changes due to both natural and anthropogenic factors have been observed to have impacts on basin morphometry with great consequences for water resources availability and water quality. Basin physical properties have direct relationships with water resources availability, and consequently, any change in stream properties can translate to reduction or increase in water yield and availability [11] [10]. Also, a high variability of rainfall characteristics (intensity, duration and frequency) is becoming more pronounced within the study area; a condition that is impacting seriously on raw water abstraction at Ishashi Intake [10] from the urban sub-catchments in Lagos.…”

“…Basin physical properties have direct relationships with water resources availability, and consequently, any change in stream properties can translate to reduction or increase in water yield and availability [11] [10]. Also, a high variability of rainfall characteristics (intensity, duration and frequency) is becoming more pronounced within the study area; a condition that is impacting seriously on raw water abstraction at Ishashi Intake [10] from the urban sub-catchments in Lagos. In addition to impacting on water availability, urbanization is also impacting on other hydrological responses of the catchments including runoff, peak flow and water quality, thereby, contributing to the non-stationarity or otherwise of the catchment [10].…”

“…These observed changes can be attributed to both natural and anthropogenic factors. The core anthropogenic factor bringing changes into these sub-urban catchments is urbanization [8] [9] [10].…”

“…Going by the observable changes taking place in the Owo River catchment, this paper therefore examines the complex interactions and feedbacks leading to changes in the hydrological and morphological characteristics of the Owo River system [10]. The paper analyses the future ability of this semi-urban watershed to sustain water supply in both qualitative and quantitative terms in the face of cumulative environmental change [10]. Specifically, the paper examines the land use land cover and Morpho-dynamic changes of the Owo River catchment to identify the impacts of urbanization (anthropogenic activities) on the catchment.…”