Remote sensing for improved water and land productivity in Agriculture using WaPOR.
Introduction
A report published by the United Nations estimated 2Billion people to have faced food insecurity world wide in 2019. This shows that food insecurity still is a big challenge as much as we look forward to achieving SDG 2(End Hunger , achieve food security and improve nutrition and promote sustainable agriculture) by 2030. Food insecurity is expected to keep raising. It is highly attributed to climate change and increase of world population, we have more mouths to feed yet we have challenges in producing more. Climate change has resulted to change and fluctuations in rainfall patterns, drought and rising temperatures affecting planting seasons in such a way that there is a delay to start of planting season and change of length of planting seasons.
Water is scarce, we are experiencing longer drought seasons but there is still need to produce food, So how do we make sure that each drop of these scarce resource counts in the agricultural sector? How do we maximize yield production while using limited amount of water in our farms? This equates to Water and Land Productivity.
For the past few months, I have had an opportunity to interact with an open source tool for remote sensing data known as WaPOR(Water Productivity through Open access of Remotely sensed derived data). This is a database developed by FAO to monitor water productivity. The cloud based platform provides near real time data starting from the year 2009. The data is acquired from several satellite images such as Modis, Landsat sentinel and CHIRPS. Various dataset on the portal include: water, land, water productivity, climate and ancillary data(NDVI layers).
The datasets are available at different spatial resolution scale, ranging from 250m, referred to us continental level scale, this covers the whole of Africa and part of middle East, 100m which is referred to us national level it covers a few countries in Africa and the middle East, 30m also called the sub national level this covers a few specific areas in a few countries in Africa, Yemen and Sri Lanka. Other spatial data resolutions include, 25km for reference evapotranspiration layer and 5km for precipitation layer by CHIRPS. The temporal resolution of the data ranges from a day, dekadal (10 days), monthly to annually.
What can we do with the WaPOR.
With Wapor datasets we can monitor water use efficiency, water adequacy and water uniformity of a crop land under study. The platform allows us to download raster data directly from the portal, for use in our projects, these data can be analyzed in QGIS, ArcMap any other GIS software, we can also carry out some analysis such as point time series, area time series, water productivity time series, analysis on the portal without necessarily downloading the data. We can also analyze the datasets on big data engine platforms such as Google earth Engine.
Below are a few example analysis you can do with the datasets available.
- Land Productivity — With land productivity wapor provides several layers such as gross biomass, net biomass , Normal Difference Vegetation Index (NDVI), and the Net Primary Product (NPP) which can intern help us calculate the actual above ground biomass (AGBM), with the AGBM and and knowledge on Harvest Index we can easily calculate yield estimation.
Yield Estimation = AGBM *HI
Below is an example of an area time series using NPP layer. The analysis is performed directly on the WaPOR portal.
With such analysis we are able to monitor for instance our forest cover as well as calculate the forest biomass, estimate the crop season etc.
- Example analysis in QGIS on Actual Evapotranspiration layer(Total water consumption)
By downloading the Raster files directly from the database and performing raster analysis on QGIS the visualization can give very useful information about any area of interest, below is an example of Actual evapotranspiration in QGIS
From the image above you can clearly make a distinction between areas with higher total water consumption and lower total water consumption
- Example analysis on Google Earth Engine
Apart from the using the data on the two platforms above, WaPOR also allows us to import data directly into Google Earth Engine,
2. Water productivity — With water productivity WaPOR provides datasets such as the actual evapotranspiration, transpiration, reference evapotranspiration and water productivity. Using the reference evapotranspiration layer we can estimate the potential evapotranspiration, with this layers we are able to estimate other water use efficiency parameters such as water adequacy, water uniformity, water relative deficit and water Beneficial fraction. For instance below is a map showing Adequacy which is estimated as the ratio of seasonal actual evapotranspiration (ET a) to seasonal potential evapotranspiration (ETp)
Conclusion and Recommendations.
WaPOR is a resourceful database in this era where there is need to make each drop of water count. It is well suited for large scale irrigation schemes considering most areas fall under the 100m pixel spatial resolution. with some few areas under 30m pixel spatial resolution more in-depth analysis can be done to monitor water productivity in these areas.
More to it, the databases is free as well as tools to help us navigate the analysis on water and land productivity . The scripts are freely available through the links shared below. This is a tool that more irrigation schemes should pick up to help in monitoring daily irrigation scheme operations to enhance both the water and land productivity.
References and Resources
Chukalla, A.D., Mul, M., Tran, B., Karimi, P. Standardized protocol for land and water productivity analyses using WaPOR (v1.1). Zenodo. http://doi.org/10.5281/zenodo.4641360, October 2020.
Waporact scripts to help perform irrigation performance indicators https://github.com/eLEAF-Github/WAPORACT
Water Productivity Master class series available on WaterPIP videos YouTube and the Water Channel website
