Climate Change Adaptation Technologies for Water A practitioner’s guide to adaptation technologies for increased water sector resilience WATER ADAPTATION TECHNOLOGY BRIEF

Rainwater harvesting for infiltration

Challenge: Too little water Adaptation response: Water augmentation

Description Rainwater harvesting for infiltration, also known as in situ water harvesting, is a practice in which rainwater uptake in soils is increased through the soil surface, rooting system and groundwater. Soil effectively acts as the storage agent, which improves water holding capacity and fertility and reduces risks of soil loss and erosion. Common examples of water harvesting practices include terracing, pitting and conservation tillage. Due to variable and unpredictable weather patterns this technology has served as an important water source for agriculture in civilizations for centuries. This technology plays an important role in climate change adaptation due to increases in unpredictable weather patterns. Apart from its predominant function of improving cropland and vegetation, it can also help ensure sustainable water supplies for livestock or domestic use through improved recharge of nearby water-flows or ponds, as well as groundwater. Implementation When selecting a water harvesting site, possible quality and quantity downstream consequences should be considered by conducting hydrological modelling and analyses of watershed level impacts, if appropriate). These analyses, combined with data on local temperature and rainfall patterns, can then inform siting and selection of a water harvesting approach (e.g. terracing, pitting, etc.). For establishment of a rainwater harvesting system, digging and transportation of soils to or from the site may be necessary, in addition to regular monitoring and maintenance for maintaining infiltration capacity. Environmental Benefits - Increases infiltration and recharge, soil fertility and water holding capacity of soils. - Reduces risk of soil erosion and loss. Socioeconomic Benefits - Decreases risk of soil erosion (thus reduced loss of nutrients) and improved irrigation supports food security and improves drought resilience. - Maintains cultural heritage for some communities that historically practiced rainwater harvesting for infiltration. - Increases harvests and avoids losses due to soil degradation.

Opportunities and Barriers Opportunities: - Low cost technology - Flexible infrastructure - Directly benefits local communities - Relatively simple to establish and maintain Barriers:

Download full publication from: http://www.unepdhi.org/publications Climate Change Adaptation Technologies for Water A practitioner’s guide to adaptation technologies for increased water sector resilience WATER ADAPTATION TECHNOLOGY BRIEF

- Perceived lack of direct economic benefit from harvested rainwater - Local restrictions regarding rainwater harvesting may exist - Care must be taken to understand and estimate the hydrological impacts of such practices on local water systems - Large scale impacts may be difficult to achieve (land requirements and siting on private vs. public lands) - Large water harvesting systems can have negative effects on runoff and groundwater levels, which in turn can affect ecosystem dynamics and downstream users

Implementation considerations* Technological maturity: 5 Initial investment: 1-3 Operational costs: 1-2 Implementation timeframe: 1-2

* This adaptation technology brief includes a general assessment of four dimensions relating to implementation of the technology. It represents an indicative assessment scale of 1-5 as follows: Technological maturity: 1 - in early stages of research and development, to 5 – fully mature and widely used Initial investment: 1 – very low cost, to 5 – very high cost investment needed to implement technology Operational costs: 1 – very low/no cost, to 5 – very high costs of operation and maintenance Implementation timeframe: 1 – very quick to implement and reach desired capacity, to 5 – significant time investments needed to establish and/or reach full capacity This assessment is to be used as an indication only and is to be seen as relative to the other technologies included in this guide. More specific costs and timelines are to be identified as relevant for the specific technology and geography.

Download full publication from: http://www.unepdhi.org/publications Climate Change Adaptation Technologies for Water A practitioner’s guide to adaptation technologies for increased water sector resilience WATER ADAPTATION TECHNOLOGY BRIEF

Sources and further information

Agriwaterpedia (2016). Available at: http://agriwaterpedia.info/wiki/Rainwater_harvesting

Batchelor, C. and others. (2011). Life cycle costs of rainwater harvesting systems, Occasional Paper 46. The Hague, The Netherlands: IRC International Water and Sanitation Centre, WASHCost and RAIN. Available at: http://www.ircwash.org/sites/default/files/Batchelor-2011-Lifecycle.pdf

CVC & TRCA (2010). Low Impact Development Stormwater Management Planning and Design Guide, Version 1, Credit Valley Conservation Authority and Toronto and Region Conservation Authority. Available at: http://www.creditvalleyca.ca/wp-content/uploads/2014/04/LID-SWM-Guide-v1.0_2010_1_no-appendices.pdf

Rainwaterharvesting.org (2016). Available at: http://rainwaterharvesting.org/

Studer, R.M. and Liniger, H. (2013). Water Harvesting Guidelines to Good Practice. Centre for Development and Environment (CDE) and Institute of Geography, University of Bern; Rainwater Harvesting Implementation Network (RAIN), Amsterdam; MetaMeta, Wageningen; The International Fund for Agricultural Development (IFAD), Rome. Available at: https://www.wocat.net/fileadmin/user_upload/documents/Books/WaterHarvesting_lowresolution.pdf

UNEP (2014). Green Infrastructure Guide for Water Management: Ecosystem-based management approaches for water related infrastructure projects. UNEP-DHI, IUCN, TNC, WRI, Green Community Ventures, U.S. Army Corps of Engineers.

Download full publication from: http://www.unepdhi.org/publications