TY  - THES
T1  - Aquacrop and ensemble global climate models for rice production under climate change impact
A1  - Ali, Houma Abdusslam Ahmad
LA  - English
YR  - 2021
UL  - http://discoverylib.upm.edu.my/discovery/Record/oai:psasir.upm.edu.my:92922
AB  - Lowland paddy rice in Northwest Selangor, particularly in Tanjong Karang Rice
Irrigation Scheme (TAKRIS), is the main crop grown during July to October
(wet/main season) and January to April (dry/off-season). Climate change is one of
the main environmental problems of the current century that directly affects growing
conditions of most crops, including rice. This study evaluated the impacts of climate
change on rice production in an area within TAKRIS. FAO-AquaCrop model was
applied under 18 General Circulation Models (GCMs) with three levels of climate
sensitivity (RCP4.5, RCP6.0 and RCP8.5) to assess yield potential of rice.
Future projections of multi-GCMs in the study region have shown that temperature
will increase under all emission scenarios, with the largest changes during the dry
season. Compared to the baseline period (1976 to 2005), the projected increase in
maximum temperature ranges from 0.6 to 1.5°C during the 2020s, 0.5 to 1.7°C
during the 2050s and 0.7 to 3.01°C during the 2080s period and that in minimum
temperature ranges from 0.7 to 1.7°C during the 2020s, 0.6 to 1.8°C during the 2050s
and 0.8 to 3.2°C during the 2080s under RCP4.5, RCP6.0 and RCP8.5 scenarios,
respectively. Rainfall projections show average changes of –0.3% during the 2020s,
–0.22% during 2050s and –3.25% during the 2080s for the dry season, and 7.6%
during 2020s, 6.8% during 2050s and 11% during the 2080s for the wet season under
RCP4.5, RCP6.0 and RCP8.5, respectively.
In order to calibrate and validate the AquaCrop model, version 1.6, intensive field
investigation was done in a paddy plot at Sawah Sempadan compartment of the
TAKRIS during the main and off-seasons of 2017. Data related to developmental
stages of plants and yield was measured; historical data were collected from
secondary sources. Water balance components were analyzed from the field observations of a paddy field. Irrigation water accounted for 59.6% of the total water
input (irrigation and rainfall) during the off season and 76.2% of the total water input
during the main season. Rainfall contributed 40.4% and 23.8% of total water input
in the corresponding seasons. The grain yield of rice was 5.5 t/ha for the off-season
and 5.9 t/ha for the main season. The model was validated with performance
indicators of normalized root mean square error (2< NRMSE <4), prediction error
(0.75<Pe<3), mean absolute error (120<MAE<160), and index of agreement
(0.5<d<0.8). Satisfactory simulation results were obtained for biomass, (grain) yield
and productivity. The average yield is projected to increase by 7.7%, 10.2% and
17.3% from baseline period in the off-season, and 8.6%, 11.5% and 18.4% in the
main season under RCP4.5, RCP6.0 and RCP8.5, respectively. Simulation results
also reveal that poor weed control measures and water stress conditions will reduce
rice yields in the future. Under worst weed control, grain yield is expected to drop
by 67% compared to weed-free condition.
Simulation results suggest that crop evapotranspiration (ETc) is likely to decrease
under all climate scenarios during both seasons, the maximum decrease being up to
10% under RCP8.5. Annual effective rainfall is predicted to increase marginally.
Therefore, irrigation water requirement is projected to decrease by 3.5% in offseason
and 5.5% in main season. Water productivity for continuous flooding shows
an increasing trend in both off and main seasons, with the most significant increase
under RCP8.5. Water productivity, based on irrigation plus effective rainfall
(WPIrr+ER), is predicted to increase by 18%, 20% and 21% in off-season and 16%,
18% and 21% in main season under RCP4.5, RCP6.0 and RCP8.5 scenarios,
respectively. Water productivity, based on crop evapotranspiration (WPETc), is
predicted to increase by 22%, 23% and 26% in off-season, and 18%, 19% and 22%
in main season under RCP4.5, RCP6.0 and RCP8.5 scenarios, respectively. Thus,
AquaCrop simulation revealed a rising trend of potential rice yields and irrigation
needs in conjunction with a CO2 fertilization. Suppressing stress on yield under
rising temperature has been compensated by the ensuing increased CO2 fertilization.
Moreover, proper weed control and water management practices have augmented
yield under changing climate. This study would provide intuitive knowledge for
Tanjung Karang Rice Irrigation Scheme for the development of sustainable
productive rice yield under different management and environmental conditions.
KW  - Crops and climate
KW  - Rice - Climatic factors
ER  -