New GIS tool to support decision making in catchment restoration
Rob Nieuwenhuis reveals CROM DSS, an application that links science with participatory processes. The tool helps field operators to identify priority sites for soil erosion and landslide mitigation – and then guides their response.
Soil erosion has become a very big issue in Africa and other regions around the globe, particularly in those developing countries where pressure on land is extremely high and forests are cut away. Hillsides are increasingly taken for agriculture to provide the food for a growing population, using unsustainable methods such as hillside farming, instead of more resilient terracing and agroforestry. This short-term approach leads to exposed soil that can be eroded by rain and even high winds. The result is an increased risk of landslides and also a lack of fertile topsoil for agriculture. Despite the apparent availability of land, these factors create ‘wet deserts’ that fail to provide for local populations.
For Rwanda – the land of a thousand hills – this challenge is particularly pressing, as so much of the agriculture is on hillsides, and farmers cultivate crops for up to three seasons of the year. The deep brown colour of the rivers is clear evidence of the high sediment loads that can make the water unfit for drinking and also hydro power.
As a systems scientist with Mott MacDonald, I take a keen interest in those ‘nexus’ issues that have a damaging impact across the three key areas of climate resilience: food security, water security and energy security. I was deputy team leader for the ‘Water for Growth Rwanda’ programme, which aimed to reverse the rate of soil erosion in four key catchment areas and set a blueprint for equitable, efficient and environmentally sustainable water resources.
Adding value
We worked in close collaboration with the Government of Rwanda, using integrated water resource management (IWRM) techniques to identify and then take action at priority sites. Previously, the districts’ selection of areas to be restored lacked transparency and a clear rationale. When they asked us to come up with some landscape restoration ‘opportunity maps’ for the four catchment areas, we recognised the potential in developing an evidence-based decision support tool that would answer the same question for the entire country.
The result is CROM DSS (or ‘Catchment-based landscape Restoration Opportunity Mapping Decision Support System’ if you want the full title!). We partnered with ESRI Rwanda to develop a practical, standardised tool in ArcGIS 10.5, using the software’s model builder.
The tool consists of a geo-database and a series of automated processes that identify risks, locate existing protection, assess priority areas, and classify land according to slope and soil depth – with the ultimate aim of identifying suitable restoration options.
This information feeds into detailed local consultation and decision-making processes that guide the development of a restoration map at district, catchment, or micro-catchment level (the latter covering around 500 ha).
CROM DSS is proving extremely popular with the government, who have made the tool obligatory to support decision making, as well as monitoring and reporting, for the national soil erosion strategy, in support of the multi-billion investments required to restore Rwanda’s catchments. Officials can now target erosion control measures with certainty and also inspect if contractors are doing what they promised to do.
Connecting theory and practice
The tool has helped the government to develop catchment plans for 30% of the country’s surface area, including detailed water allocation plans that are mapped out across different lengths of time up to 2050. The ministry now knows exactly how much water can be allocated to irrigation, industry, livestock, domestic water supplies and to the environment.
The game-changing aspect of CROM DSS is that it links scientific research to participatory decision making. It uses widely available digital technology to reveal problems with accuracy and then guide the response on the ground. That combination of lab-based theory and real-world action is unique in integrated water resource management.
Due to the lowering costs of technology, the development of CROM DSS for the whole of Rwanda was actually more affordable than commissioning the four localised opportunity maps. The system is also easy to improve incrementally and to update with new information. At Mott MacDonald, we have recognised the potential to reformat this tool elsewhere in the world, and we are already taking it to other development programmes in Nepal and Tajikistan.
The clock is ticking…
Rwanda is in a race against time, not least as climate change is starting to bite in a country where 90% of the population are employed in farming. This beautiful land is already Africa’s most densely populated country – and numbers are expected to double in the next 20 years. The demand on natural resources is expected to triple by 2040.
In the dry season, droughts are becoming more commonplace and severe. The wet season is becoming concentrated into heavy downpours, rather than constant daily rain. These deluges contribute to worrying levels of soil erosion, which is believed to cost the country 20-200% of GDP annually. For a land-locked nation, which already relies heavily on imports, such a failure would prove catastrophic. Rwanda’s hopes of becoming a middle-income economy by 2035, and then high-income status by 2050, could be washed away.
Having seen the work on the ground, however, I am still optimistic that Rwanda may yet win its battle against soil erosion. Water managers and water users are increasingly working together and it’s encouraging to see communities taking responsibility for catchment restoration and sustainable land husbandry, such as by planting trees on terraces and protecting riverbanks. This is a totally new approach in Rwanda. One day, I hope the rivers will run blue again.