PyWaPOR OpenCourseWare

Converting NPP to biomass production and yield

One of pyWaPOR's outputs are the NPP layers, to convert them into biomass production and crop yield you can convert NPP using crop specific parameters. This is described below 

Estimating biomass production

The NPP layer is used to calculate yield for a specific crop. The methods used for the analyses are derived from Chukalla et al. (2022). Biomass production can be derived from the WaPOR data using the following equation (FAO and IHE Delft, 2019):

where mc [–] is the moisture content of the fresh biomass, fc [–] is the light use efficiency (LUE) correction factor calculated by dividing the LUE of the crop (in this case sugarcane) by the LUE of a generic crop type that WaPOR NPP layer uses (2.7 MJ g−1 biomass; FAO, 2020), and AOT [–] is the ratio of above-ground over total biomass. B and Y can be expressed in tonnes per hectare (t ha−1), by dividing the amount in kilograms per hectare by 1000. 

Estimating crop yield

Crop yield is calculated by multiplying the biomass by the harvest index (Hi [–]):

The crop yield is calculated over the cropping season (from the start to the end of the cropping season. The crop parameters used in these equations for sugar cane are presented in Table 1. For different crops many of these crop parameters can be obtained from the sources indicated in the table. 

Table 1 Parameters used for calculating sugarcane yield (Source: Chukalla et al., 2022)

Estimating crop water productivity

Crop water productivity is calculated as the ratio between the crop yield and actual evapotranspiration.

Note: these calculations are done for the cropping season and per crop 

An overview of typical crop parameters can be found below

More information on different water productivity concepts and more can be found in the MOOC Water Productivity in Practice

References

FAO and IHE Delft, 2019. WaPOR Quality Assessment – technical report on the data quality of the WaPOR Database version 1.0. FAO report, Rome, Italy (http://www.fao.org/3/ca4895en/ca4895en.pdf)

FAO, 2020. WaPOR database methodology: Version 2 release, April 2020. Rome. https://doi.org/10.4060/ca9894en

Steduto, P., Hsiao, T.C., Fereres, E. and Raes, D., 2012. Crop yield response to water (Vol. 1028, p. 99). Rome: fao. https://www.fao.org/3/i2800e/i2800e.pdf

Villalobos, F. J. and Fereres, E.: Principles of agronomy for sustainable agriculture, Springer, New York, USA, ISBN 978-3-319-46116-8, 2016.

Additional materials

Giordano, M.; Turral, H.; Scheierling, S. M.; Tréguer, D. O.; McCornick, P. G. 2017. Beyond “more crop per drop”: Evolving thinking on agricultural water productivity. Colombo, Sri Lanka: International Water Management Institute (IWMI); Washington, DC, USA: The World Bank. 53p. (IWMI Research Report 169). [doi: 10.5337/2017.202]

Molden, D.J., Sakthivadivel, R., Perry, C.J. and De Fraiture, C., 1998. Indicators for comparing performance of irrigated agricultural systems. IWMI Research Report 20.

Seijger, C., Chukalla, A., Bremer, K., Borghuis, G., Christoforidou, M., Mul, M., Hellegers, P. and van Halsema, G., 2023. Agronomic analysis of WaPOR applications: Confirming conservative biomass water productivity in inherent and climatological variance of WaPOR data outputs. Agricultural Systems, 211, p.103712.

List of water productivity related capacity building materials

• MOOC on Water Productivity assessment using WaPOR (English)
• MOOC on Water Productivity in Practice
• Webinars as part of WaterPIP project - Water Productivity Masterclass Series 

List of water productivity related projects

• Water Productivity Improvement in Practice (WaterPIP)- https://waterpip.un-ihe.org/
• Using Remote Sensing in support of solutions to reduce agricultural water productivity gaps (WAPOR)- https://wateraccounting.un-ihe.org/wapor-phase-2
• Expanding support to Water Accounting in River Basins and Water Productivity Measurements in Irrigation Projects (ADB WA)- https://wateraccounting.un-ihe.org/adb-wa-phase-2
• Rapid Assessment of the Water Accounts in Lake Urmia Basin, Iran (WA-Urmia)- https://wateraccounting.un-ihe.org/wa-urmia
• Demonstrating Water Accounting and Water Productivity analyses to support Country Water Assessments (ADB WA)- https://wateraccounting.un-ihe.org/adb-wa-phase-1