The concept on rainwater management strategies at landscape scale


In the Nile Basin Development Challenge, a rainwater management practice, hereafter referred to as practice, is defined as anything done by a farmer or a rural community to increase water retention or water productivity within a watershed. This definition assumes that a farmer or a group of farmers takes the decision to do something on their farm or land. As such it includes a broad range of practices such as water harvesting, soil and water conservation, livestock production, small scale irrigation, reforestation, agro-forestry or grassland management.
When implemented, many of these practices might increase the amount of water available within the watershed, enabling farmers and community downstream to adopt new practices. To take these synergies within a watershed into account, single practices need to be combined and bundled into rainwater management strategies that maximize water retention or water productivity at a specific landscape scale.
In ecology, the landscape is a scale. It represents a proportion of heterogeneous land composed of sets of interacting ecosystems that are repeated in a similar fashion in space. In the context of water management, the landscape scale can be understood as a watershed, that comprises a top slope (upland), a middle slope (midland) and the bottom valley (lowland), as shown in Figure 1. From this perspective a landscape approach to rainwater management suggests that synergies occurred by combing practices within a watershed are assumed constant. Impact on downstream watersheds can be assessed by hydrological models.
conceptual_landscape.png
We define a rainwater management strategy at landscape scale corresponds to a bundle of practices that cover the whole gradient of the landscape (upland, midland, lowlands) and maximizes water retention or water productivity within the landscape (micro-watershed or sub-basin). To maximize water productivity and water retention within the landscape, a RMS needs to fulfill deferent objectives at different locations in the landscape. Table 1 shows the major objective of a suitable RMS at a given location in the landscape.
Table 1 : objectives of practices in the different zones and land use

Main objective(examples)
Zone
Cropland
Grassland
Degraded land
Uplands
Increase infiltration
(All forms of forestry, percolation pits)
Increase the quantity and quality fodder for livestock
(over sawing, area exclosure)
Rehabilitated degraded land
(half moon, forestry)
Midlands
Increase soil and water conservation
(bunds, terraces, in situ water harvesting)
Lowlands
More efficient use of surface or shallow water
(Wells, rivers
Independent
Increase water availability in the dry season
(Ex-situ water harvesting)

In the uplands, the objective could be to increase water infiltration, mid elevation land practices could aim to increase in-situ soil and water conservation. In the lowlands the objective of a practice could be a more efficient use of surface and shallow water. Ex-situ water harvesting techniques can be applied everywhere across the landscape where water can be collected and used for supplementary irrigation or for livestock.
Next to practices that are closely related to farmers’ decision making, interventions are defined in this game as anything done by a government or NGO’s or any other actor to initiate a practice change. Note that these definitions differ from the ones used in environmental sciences where the word intervention refers to any practice that intervenes on the landscape structure.

Rainwater management practices

The game was designed to validate and build upon an initial database of existing and potential RMS practices in the Blue Nile Basin. Developed through literature review and expert knowledge acquired through stakeholder participation, for each practice it provides information about its purposes as well as any bio-physical, socio-economic and institutional condition of success. For this database, RMS were defined very broadly to include traditional water-crop related practice, agro-forestry and livestock oriented practices.
Bio-physical conditions suitability conditions are relatively well defined in the literature (Desta et al., 2005). Socio-economic suitability is less well understood and sometimes contradictory (Amha, 2006; Deininger and Jin, 2006; Deressa et al., 2009; Hagos, 2010; Petros, 2010). These conditions have been validated in several expert meeting. When contradictory conditions were found, the one suggested by the experts was retained.
From this database, half of practices were used to develop the game. The selection of these practices was based on the potential impact, as well as their relevance in current policy and NGO work.