Estimating the water requirement of grapevines in Iran in the coming decades

Estimating the water requirement of grapevines in Iran in the coming decades



Introduction

It is predicted that the impact of climate change on agriculture will be more severe in the coming years due to changes in the intensity, magnitude and distribution of rainfall, soil water content, atmospheric water vapor, higher temperatures and, as a result, more evaporation and transpiration. This will have significant implications for irrigation needs, especially in semi-arid regions, known as hotbeds of climate change. Grape production requires a large amount of water, which can be problematic in semi-arid Mediterranean regions, where climate change projections predict a decrease in water availability associated with decreased rainfall and increased temperature (Pizaro et al., 2022: 1).



Materials and Methods

In the basic period, the status of effective climatic parameters was first investigated. Then, the time of occurrence of the phenological stages of the grapevine at the regional level was determined based on the data of the observation period. For future period data, the downscalled data of MarksimGCM database was used. The ordinal kriging method was used for spatial distributions. RCP8.5 and RCP4.5 scenarios were used as pessimistic scenario and moderate scenario. In order to identify the phenological stages of grapevines, studies and field visits were conducted on grapevines. To control the phenological stages of grapes, the BBCH scale was used at Golmkan Agricultural Meteorological Station located in Khorasan Razavi Province in Northeast Iran during a complete growth period from the beginning of germination to the end of the stagnation period. In fact, the codes of phenological stages were observed and recorded in the field. In addition to field observations, climate data from the Golmakan agricultural meteorological station was also used. Golmkan agroclimate station is located near Golmkan village and on the side of Mashhad-Chenaran road with an altitude of 1176 meters above sea level. This station mainly measures the effect of weather parameters on wheat and grape crops.

Results and discussion

The results showed that the grape tree in the initial stage of growth has a lower water requirement than other stages of growth. In the initial stage, the amount of water required varies from 207 mm in high and cool areas to 303 mm in low altitude and hotter areas. The results showed that in the coming decades, the amount of water needed will gradually increase compared to the base period. Based on the RCP8.5 scenario, in the period (2020-2055) and (2056-2090), the water demand will increase by 2.6 and 12 mm, respectively, compared to the base period. The amount of increase in water requirement in low altitude areas will be higher than in high and cool and cold areas. According to the RCP4.5 scenario, the amount of water needed in the period (2020-2055) and (2056-2090) will increase by 4 and 8 mm, respectively, compared to the base period. The amount of changes in water demand will be less than in the pessimistic scenario. The results of the spatial distribution of water requirement in the middle stage of grape growth in the base period showed that altitude conditions play a major role in the spatial distribution of water requirement in the middle stage of growth. The lowest amount of water requirement is observed in high areas. In the basic period, the amount of water needed in grape growing areas varies from 586 mm to 859 mm. The middle stage of grape growth, because it corresponds to the hot months of the year, has the highest amount of water needed in the growing season of grapes.

The results of the changes in the water requirement of the middle stage of grape growth in the coming decades compared to the base period under the RCP8.5 scenario show that in the period (2020-2055) and (2056-2090), on the water requirement of the middle stage of growth Grapes will increase 25 and 50 mm respectively, in its cultivation areas in Iran. In the far future period, the amount of water needed is higher than in the middle future. The highest amount of water requirement will be observed in low altitude stations

The results showed that in the period (2020-2055), the water requirement will change from 611 mm in high and cool areas to 884 mm in low and hotter areas. In the period (2056-2090), the water requirement will increase from 636 mm to 909 mm according to the altitude conditions.

The results of changes in the water requirement of the middle stage of growth based on the RCP4.5 scenario for future periods showed that in the period (2020-2055) and (2056-2090) the amount of water requirement will be increased by 10 and 20 mm, respectively. The increase in water demand in this scenario will be less than the pessimistic scenario. The highest amount of water requirement will occur in low altitude areas.

The results showed that in the period (2020-2055), the water requirement will increase and change from 596 mm in high and cool areas and up to 869 mm in low altitude areas. In the period (2056-2090), the amount of water required for the middle stage of growth will change increase from 606 to 879 mm according to the altitude conditions. The results of the spatial distribution of the water requirement of the final stage of grape showed that in the basic period, the amount of water requirement varies from 358 to 410 mm from high to low altitude areas. This stage has less water requirement than the middle stage of growth. The lowest water requirement is observed in the high and cool areas of the northeast, north and northwest, and the high Zagros region. The areas of the plains and the marginal slopes of the mountainous areas have a higher water requirement.



Conclusion

The results show that in the RCP8.5 pattern, in the coming decades (2020-2055) and (2056-2090), 31 and 98 mm will be added to the reference evapotranspiration rate, respectively. The results of simulated data processing showed that under the RCP8.5 and RCP4.5 scenarios in the future periods, the amount of water requirement will increase compared to the base period for the growing stages of grapes in the growing areas of Iran. So that in the initial stage of growth under the mentioned scenarios in the periods (2020-2055) and (2056-2090) the amount of water requirement will increase by 6.2, 12, 4 and 8 mm, respectively. The water requirement of the middle stage of growth in the future period will increase compared to the base period. Considering the timing of this stage of grape growth with the warm days of the year, the amount of water requirement is higher than other stages of grape growth. The lowest and the highest amount of water requirement will occur in the low and high altitude areas, respectively. The highest amount of water requirement in the stages of grape growth in the coming decades will occur in the low altitude areas on the edge of the high areas in the grape growing areas. The lowest water requirement in the future will occur in the high and cold regions of the northwest, the high Zagros and the Alborz regions and the high regions in the east and southeast.