The climate in the Yellow River Basin has undergone significant changes in recent years, which has a significant impact on surface hydrological and ecological processes in the basin. Studying the spatial and temporal variation of evapotranspiration in the Yellow River Basin is indicative for understanding deeply land-atmosphere interactions and regional water resources management. In this paper, the appliability of ERA5-Land evapotranspiration in the Yellow River Basin was evaluated using in-situ observations of Haibei, SACOL (Semi-Arid Climate and Environment Observatory) and Yucheng stations which are selected as representative stations from the source region, Hetao region and the lower reach of the Yellow River Basin, respectively. Then based on monthly latent heat flux from ERA5-Land data, the spatial and temporal variation of evapotranspiration in the Yellow River Basin in the past 42 years (1980-2021) are analyzed using EOF (Emipirical Orthogonal Function), power spectrum and regression analysis methods. The results show that ERA5-Land data can reflect the variation characteristics of evapotranspiration at Haibei, SACOL and Yucheng stations with good correlation and small error and root mean square deviation, which is applicable for the analysis on spatial and temporal variation of evapotranspiration in the Yellow River Basin. There are multi-timescale variations of evapotranspiration in different regions of the Yellow River Basin, with significant oscillation periods of main 5 a and 15 a, and obvious inter-annual and inter-decadal variations. The first mode in different regions of the Yellow River Basin characterizes the consistency in spatial distribution, which decreases around 2004. The second mode is dipole distribution, indicating the reverse change in space. The deceleration of evapotranspiration in the Yellow River Basin in the past 42 years is not same in different regions, with the fastest rate of -3.74 mm·a^-1 in the lower reaches and -2.82 mm·a^-1 in the Hetao area, while the deceleration in the source area is relatively gentle. The summer evapotranspiration variability is the largest, and the deceleration is faster in the Hetao area and the lower reaches. The winter evapotranspiration variability is smaller, but the source area has the largest winter evapotranspiration deceleration of -0.48 mm·a^-1.

As the fourth major staple crop after rice, wheat and corn, potato is of great significance for ensuring the national food security. In order to explore the response characteristics of potato (Solanum tuberosum L.) yield, leaf photosynthetic physiology, dry matter accumulation characteristics to water stress in the semi-arid region of the Loess Plateau, the soil water stress experiment was conducted in 2021 by using the main potato variety “Xindaping” as the test material. The soil water was controlled during the critical period of tuber enlargement (August). Field water capacity was set at 40%±5% (moderate water stress, T1 treatment) and 55%±5% (mild water stress, T2 treatment), and 75%±5% (full water treatment, T3) was used as the control for analysis. The results show that under water stress, the maximum tuber weight per plant, tuber weight per plant and yield all decreased, the number of tubers decreased, the weight and the number of pellet potato increased significantly (P<0.05), and compared with T3 the yield of potato under T1 and T2 treatments decreased by 30% and 13%, respectively. The net photosynthetic rate (P_n), stomatal conductance (G_s) and intercellular CO₂ concentration (C_i) of potato leaves decreased significantly, among them the G_s decreased by 59%, and the water use efficiency (WUE) of T1 treatment was 31% higher than that of T3. In the weak light area, the effect of moderate and mild water stress on P_n is not obvious (P>0.05), when the light intensity was higher than 300 μmol·m^-2·s^-1, the differences between treatments increased, and P_n under T1 and T2 treatments decreased by 42% and 32% on average compared with T3. Under the influence of water stress, the maximum net photosynthetic rate (P_nmax), light compensation point (LCP) and dark respiration rate (R_d) decreased significantly (P<0.05), and light saturation point (LSP) under mild water stress was the highest (893.32 μmol·m^-2·s^-1). The range of available photosynthetically active radiation (PAR) of leaves decreased under moderate water stress, and the ability to use strong light decreased. The dry matter weight of roots, stems, leaves and petioles decreased under water stress, and under moderate water stress, the petiole decreased the most (63%), followed by leaves (57%) and roots (50%). This study can provide theoretical basis for potato drought damage assessment and soil water efficient utilization in semi-arid area of Loess Plateau.

In order to explore the response mechanism of photosynthetic physiological process of spring maize to soil water and temperature changes in semi-arid region of the Loess Plateau under the background of climate change, taking spring maize as the research object, the pot water control experiment was carried out in the Dingxi Arid Meteorology and Ecological Environment Experimental Base of China Meteorological Administration in 2017. Control treatment (CK treatment, soil moisture at 80% of field water capacity) and water treatment (WS treatment, soil moisture at 45%-50% of field water capacity) were set at spring maize seven-leaf stage. Three leaf temperature gradients were set, which were optimum temperature 25 ℃, high temperature 35 ℃ and extreme high temperature 40 ℃ (CK treatment corresponds to CK-25, CK-35 and CK-40; WS treatment corresponds to WS-25, WS-35 and WS-40). The response characteristics of leaf gas exchange parameters and water use efficiency to soil moisture and temperature changes at seven-leaf stage of spring maize were analyzed. The results show that within a certain range of photosynthetically active radiation (PAR), the net photosynthetic rate (P_n) of leaves gradually increased with the increase of PAR. When water supply was insufficient, with the increasing of PAR, stomatal limiting factors of spring maize leaves under WS treatment transferred to non-stomatal limiting factors, and photosynthesis is inhibited obviously. The P_n of spring maize leaves under WS-35 treatment was the highest, and P_n of maize leaves under WS treatment was significantly lower than that under CK treatment in the PAR high value area. The PAR at light saturation point decreased under different temperature gradients. Compared with CK-40 treatment, the P_n of spring maize leaf under WS-40 treatment decreased significantly with the increase of PAR (P<0.05), and photoinhibition was obvious. When the water supply was sufficient, the transpiration rate (T_r) increased with temperature increasing. When the water supply was insufficient, compared with CK-40 treatment, the T_r and stomatal limitation (L_s) of spring maize leaf decreased significantly (P<0.05), while intercellular CO₂ concentration (C_i) increased significantly (P<0.05) under WS-40 treatment. With the increase of PAR, T_r decreased and water use efficiency (WUE) of spring maize treated by WS-40 was higher than that CK treatment. This study can provide reference for the physiological characteristics of spring maize in semi-arid region of the Loess Plateau under the background of climate change.

Drought is a major meteorological disaster with the highest frequency, the longest duration and the widest scope of harm in the world today, which has a huge and extensive impact on agriculture, ecology, social development and national economy all over the world. The drought is an important factor affecting agricultural production which determines the stability of crop production, further relates to the national food security. China is a large agricultural country, and also is a country with frequent drought disaster. Therefore, to improve the monitoring, forecasting and warning level of agricultural drought disaster, it is necessary to deeply understand its formation, influence characteristics, drought intensity, severity and physiological process and mechanism of crop victimization. It is also an important scientific problem to reduce and prevent drought disaster losses and improve national food security production. This paper comprehensively reviews the recent internal and overseas research progress of agricultural drought with different degrees and its impact on crop production, and explores the influence characteristics and mechanism of drought from the aspects of crop morphology, physiology, cellular and molecular levels, etc. The main indicators, indexes, methods and early warning systems in current agricultural drought monitoring are reviewed around food production to cope effectively agriculture drought. According to the new characteristics of agricultural sustainable development and drought, the current situation of drought disaster prevention and mitigation and agricultural drought coping are discussed. A series of drought coping measures both adaptation and mitigation are emphasized. On this basis, combining with the needs of national, regional and industrial development, the paper puts forward the important scientific problems, research countermeasures and the prospect of discipline development which should be emphasized in the future.

As the impact of climate warming on agro-ecosystems intensifies, the arid and semi-arid crops in the northwest, where water resources are extremely scarce, will face major challenges. In this paper, the water control starts from the corn tasseling period to the end of the growth period (T1 treatment) and the natural drought at the whole growth period (T2 treatment) in arid and semi-arid regions, the similarities and differences of the formation of drought disasters to the same crop were revealed in arid and semi-arid regions, in order to provide a theoretical basis for grasping the crop drought inducing-disaster process in different climatic regions. The results showed that different drought stresses affected significantly the plant height, leaf area and chlorophyll content of maize in arid and semi-arid regions. During the whole growth period of drought treatment, the response of maize in arid area to drought stress was more sensitive than that in semi-arid area, while T1 treatment had more significant effects on the growth of maize plant height and leaf area per plant in semi-arid rain-fed area. The leaf area per plant of maize under different drought treatments in semi-arid area showed an increasing trend from the horse chestnut stage to grain filling stage as a whole. Although drought stress reduces the leaf area per plant of maize, in order to ensure the later growth and development of plants, the increase of leaf area make up for the lack of photosynthetic yield due to drought stress. Therefore, in order to ensure the yield of maize in arid and semi-arid regions, semi-arid areas are suitable for planting varieties with strong photosynthetic capacity, arid areas are suitable for planting varieties with suitable plant height and leaf area, and the tasseling period is a sensitive period for maize growth and development to drought in semi-arid regions.

A typical dust weather process occurring in Northwest China from 23 to 25 April 2014 was simulated by using the atmospheric/chemical full coupled WRF/Chem model coupled with the dust emission module. The influence of the weight factor γ in the formulas of dust flux of Shao 2004 parameterization scheme (Shao04 scheme) on spatial and temporal distribution of dust was analyzed. The scope of simulated dust was compared with that  monitored by FY-3C meteorological satellite remote sensing and dust mass concentration simulated by the model was compared with observations, the key parameter which was more suitable in the Shao04scheme for Northwest China was determined. The results are as follows: (1) The weight factor γ  had a significant influence on the simulation of dust scope and maximum center value of mass concentration and vertical dust flux. (2) Different γ values could simulated the variation trend of PM10 and PM2.5 mass concentration well in dust weather, but only when the value was setted as 1, that is, WRF/Chem model coupled with Shao2011 sand parameterization scheme could simulate the change of PM10 and PM2.5 mass concentration more accurately during the dust process in Northwest China.

Taking Beijing as the research area,this paper used surface temperature retrieval based on ASTER (advanced spaceborne thermal emission and reflection radiometer)thermal infrared data and observed surface temperature at meteorological stations. Accuracy verification of surface temperature retrieval based on ASTER data was carried out using absolute error and relative error, and its spatial distribution was analyzed. The results show that the accuracy surface temperature retrieval during nighttime in winter with high urban heat island intensity based on ASTER data was higher than that in other seasons with weak urban heat island intensity, while in the daytime in summer with high urban heat island intensity based on ASTER was similar to that in other seasons with weak urban heat island intensity, and the surface temperature retrieval based on ASTER data was smaller than observations at meteorological station. The spatial distribution of  surface temperature retrieval based on ASTER data was consistent with that of observed surface temperature, and urban heat island intensity during nighttime in winter was higher than that in autumn.Urban heat island intensity during daytime in summer was higher than that in autumn, and during nighttime it was higher than that in the daytime.

Based on the data of winter wheat sowing test under different sowing dates and combined with the actual data of winter wheat frost damage survey in natural field, the cause of winter wheat frost damage and the effect on yield of winter wheat were analyzed in northern North China during 2017/2018. The results show that the sowing date of winter wheat was delayed to adapt to climate change. However, the sowing date should not be later than October 21 in northern part of North China. If the sowing date was postponed or the straw was returned to the field, the seeding rate should be increased to ensure the emergence rate and basic seedlings. When the varieties were promoted and produced, the winter and semi-winter varieties should be planted together to prevent the potential risk of winter wheat freezing caused by “cold winter”. The dead seedling rate during overwintering increased by 1%, and the yield decreased by about 1 kg·hm-2. The sowing period of winter wheat was affected by rainfall and more precipitation. Late sowing and poor sowing quality, differences between winter and spring characteristics of winter wheat varieties, improper use of herbicides and pesticides were the main reasons for increasing the death rate of winter frozen seedlings.