Under the background of global warming, studying the characteristics of dry-wet climate changes in the Shiyang Rive Basin and their influence on vegetation coverage has significant importance for the ecological environment construction of the basin. Based on the precipitation temperature homogenization index (S) in the Shiyang River Basin from 1971 to 2020, the spatial-temporal changes of the dry-wet climate in the basin were analyzed from the aspects of drought station frequency ratio, drought frequency, and more. Combined with the Normalized Differential Vegetation Index (NDVI) remote sensing data, the influence of dry-wet change on NDVI was analyzed. The results showed that the inter-annual and seasonal S indices showed an increasing trend in the Shiyang River Basin over the past 50 years, with the most pronounced increase in summer. The drought degree and drought occurrence area have shown a decreasing trend in the basin. The intensity of drought in the midstream and downstream were more severe compared to the upstream, with higher drought frequencies in the downstream. The annual NDVI increased with the alleviation of drought, the increase of precipitation and decrease of temperature. The precipitation in the early and middle period of growth, as well as the temperature in the middle period had a great influence on the annual NDVI. In February, May and July, the NDVI had a lag effect in response to drought.

Heilongjiang Province is the major grain production base in China, the study of drought climate characteristics in Heilongjiang Province is of great importance for scientific prevention and management of drought disasters. Based on daily temperature and precipitation data from 80 national meteorological stations in Heilongjiang Province from May to September during 1971-2020, the daily meteorological drought composite index (MCI) of Heilongjiang Province was calculated, and the spatial and temporal distribution characteristics of drought, severe drought and extreme drought days in Heilongjiang Province were analyzed. At the same time, the circulation characteristics of typical dry and wet years were further analyzed. The results show that from May to September during 1971-2020, the southern part of the Greater Hinggan Mountains and the western part of Songnen Plain in Heilongjiang Province are drought-prone areas. The number of dry days is more in the west and some areas of the central hinterland and less in the east. The inter-decadal characteristics of medium drought, severe drought and extreme drought are obvious and show a decreasing trend. The decreasing trend of medium drought was the most obvious with a rate of -1.7 d·(10 a)^-1. There are significant differences in circulation patterns between typical dry years and wet years. In typical dry years, the area west of Lake Baikal is controlled by anticyclones, while Heilongjiang is controlled by the westerly jet stream, resulting in prevailing descending airflow, which is not conducive to the intersection of cold and warm air, and the water vapor transport channel is not obvious, so water vapor is difficult to reach the Heilongjiang region. Conversely, in typical wet years, the situation is the opposite.

Based on the Ji'nan S-band dual-polarization Doppler weather radar (CINRAD/SA-D) data, combined with automatic weather station data and conventional observation data, comparative analysis of the environmental conditions are made, and emphasis is laid on the analysis of dual-polarization signatures for the Wangzhuangji storm and Da'an storm, which are short for the two extreme rainfall storms separately occurring at Wangzhuangji county of Shenxian and Da'an county of Yanzhou, Shandong on 5 and 6 August 2020. The results show that: the two extreme heavy rain occurred in the conditions of high K index, large convective available potential energy (CAPE), deep wet layer, and moderately weak vertical wind shear. In contrast, the storm relative helicity (SRH) is evidently larger for the extreme rainfall event on 6 in August. The flow structures of the storms are significantly different: the Wangzhuangji storm tilts upward and intensively diverges at high-level inducing higher storm top and specific differential phase K_DP column, while Da'an storm performs as cyclonic rotation with weaker high-level divergence. The microphysical structure varies at different levels: for the both two storms, there are high concentration of solid (liquid) particles separately above (below) -10 ℃ layer. But Wangzhuangji storm has more abundant graupels above -10 ℃ layer, a few element of liquid particles from -20 ℃ to -10 ℃ layer, and a certain amount of ice particles below -10 ℃ layer. The two storms exhibit comparable dual-polarization characteristics with moderate differential reflectivity Z_DR, bigger K_DP and correlation coefficient (CC) at low-level, which indicate that the rainfall storms constructed with abundant moderate particle size liquid raindrops are rich of water favorable for extreme rainfall.

In order to project the future climatic characteristics and their changing tendencies in different areas in Ningxia section of the Yellow River Basin, the performance of the CMIP6 models in simulating the annual mean air temperature in Ningxia are evaluated based on observation data at 19 national meteorological stations and the CMIP6 models data. Then the future air temperature changes in the Yellow River irrigation area, the middle arid area and the southern mountainous area of Ningxia under different scenarios are analyzed. The results are as follows: (1) Most models of the CMIP6 have a good simulation ability to annual mean air temperature in the Ningxia section of the Yellow River Basin, with spatial correlation coefficient of 0.603-0.930 and temporal correlation coefficient of 0.381-0.782. Meanwhile, the result of multi-model ensemble simulation is better than that of a single model. (2) Under the SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5 scenarios, it is predicted that the annual mean air temperature in the Yellow River Basin Ningxia section will present a significant warming trend from 2021 to 2099, with a warming rate between 0.09 and 0.68 ℃·(10 a)^-1. The warming rates are obviously different in different scenarios, which shows a decreasing trend under the SSP1-2.6, and firstly increasing and then decreasing trend under the SSP2-4.5, an increasing-decreasing-increasing trend under the SSP3-7.0, and an increasing trend under the SSP5-8.5. (3) It is estimated that the annual mean air temperature in the Yellow River irrigation area, the middle arid area and the southern mountainous area will reach 10.91-11.29, 9.48-9.87, 7.47-7.84 ℃ in the 2030s, respectively, and 11.46-13.21, 10.00-11.75, 7.97-9.66 ℃ in the 2060s under the four scenarios, respectively.

With the global warming, the intensity and frequency of abnormal drought and flood are increasing, to improve the understanding of drought-flood transition events and the ability of precipitation prediction in the east region of Northwest China, the circulation characteristics of drought-to-flood transition over the east region of Northwest China from spring to summer are analyzed by establishing an index based on the observed monthly mean precipitation, sea surface temperature (SST), and NCEP/NCAR reanalysis datasets during 1979-2020, and the possible influence from the Atlantic SST anomalies is also discussed. The results are summarized as follows: In spring of drought-to-flood years, the polar vortex is weaker, the Ural blocking is stronger and deeper, and the east Asian trough is deeper, which result in less precipitation in the east region of Northwest China controlled by dry and cold northwest flow. In summer, the upstream low-pressure system is active, the south Asian high is stronger and the western Pacific subtropical high (WPSH) is stronger and westward. Such circulation anomalous can lead to warm and moisture air supplement, resulting in a sharp transition phenomenon occurring in the east region of Northwest China. While in flood-to-drought years, it presents an opposite feature. From the previous winter to summer, the Atlantic tripole SST anomalies are key factors affecting the difference of precipitation between spring and summer. In spring of drought-to-flood years, the negative phase of the Atlantic tripole SST pattern stimulates a zonal teleconnection wave train, passing through the central and western Europe, Lake Balkhash, and Northeast China to the Sea of Japan, and this circulation is conducive to less precipitation in the study area. With respect to summer, the intensity of the wave train is weakened and shifts westward. Therefore, the intensity and location of the key circulation system in the middle and high latitudes are adjusted comparing with that in spring, causing more precipitation. In flood-to-drought years the opposite occurs.

Based on Coupled Model Intercomparison Project Phase 6 (CMIP6) simulation data and high resolution daily grid observation data, quantile mapping method and Taylor diagram were used to correct and evaluate the simulation values of extreme temperature index,respectively. It was found that corrected simulation value of each extreme temperature index was closer to the observation during historical reference period (1991-2010).The spatial-temporal variation characteristic of extreme temperature indies in near-term, mid-term and late-term of the 21st century relative to historical reference period in Fujian Province under SSP2-4.5 and SSP5-8.5 scenarios were analyzed. From the perspective of temporal variation, in each period of the 21st century, the extreme temperature indices in Fujian Province showed an increasing trend and the incremental value increased over time.From the perspective of spatial variation, the extreme maximum temperature (TXx) showed a trend of increasing more in northwest inland area and less in southeast coastal area.The spatial distribution of extreme minimum temperature (TNn) was similar to that of TXx, but the warming rate was slightly smaller. The summer days (Su) increased more in the southwest of Fujian, while the warm days (TX90p) increased faster in the southeast area. Based on the generalized extreme value (GEV) distribution, it was found that under SSP2-4.5 scenario, the temperature increase in three periods in the 21st century was relatively uniform and stable, while under SSP5-8.5 scenario, the temperature increase showed an accelerating trend. Under SSP5-8.5 scenario, TXx of 20-year return period in the historical period was likely to occur every year in late-term of the 21st century.

Based on the observational rainfall data in July of Ningxia, the NCEP/NCAR reanalysis data and the ERSSTv5 SST data from 1981 to 2018, the variation characteristics of precipitation in July in Ningxia and their formation causes were analyzed. This paper also discussed the influence of the equatorial Pacific SST anomaly on precipitation. The results are as follows: (1) In the past 38 years, the inter-annual variability of precipitation in July was significant, but the extremity and anomaly of precipitation both increased after 2000. (2) The 500 hPa geopotential height anomaly was low over the Balkash lake and it was high between North China, the Northeast China and the Sea of Japan in mid-high latitudes. The active low-pressure system from the Bay of Bengal to the South China Sea, coupled with water vapor transported by the southerly anomaly on 700 hPa from the Northwest Pacific, led to more precipitation in July in Ningxia. (3) Since the 21th century, the implication of equatorial Pacific SST on precipitation in July has strengthened, especially during late winter and early spring during the ENSO decaying phase. When the SST anomaly in the equatorial Pacific characterized  by a dipole pattern, namely, warm (cold) in the west and cold (warm) in the central, and the subtropical western Pacific anomaly cyclone (anticyclone) in July played an important role in transportation of water vapor. The pattern of lower in the west (east) and higher in the east (west) existed on 500 hPa height, which was favorable to more (less) precipitation and reflected the impact of the central pacific type of ENSO on precipitation in Ningxia to some extent.

The characteristics of surface air temperature，snow depth and other climatic elements gre analyzed on the basis of outputs from the Exp．1％C02 in which the atmospheric C02 concentration is increased by l％per year and Exp．50yrs in which the observed increasing atmospheric aerosol andC02 concentrations are used．We discussed the effects of the aerosol ou climate change over the Tibetan Plateau．The results show that there exists asignificant elevation dependency of surface climate warming，i．e．the warming trend increases with the elevation in a higlI—altitude region and its surroundings in spring，sUnllller，autmnn and winter in Exp．1％C02．For example，the linear warming trends of surface air temperature reach 0．29，0．36 and 0．50℃／10 a for 3 zones with elevations in the milge of 1．5—2 km，3—3．5 km and 4．5—5 km，respectively．With the climate wanning over the Tibetan Plateau，the snow depth decreases，which is nlore markedly at hish—altitude regi∞than its surroundings in Exp．1％C02．In Exp．50yrs，however，the linear warming trend of surface air temperature is weak，though it is prominent at high elevations than at low elevations in the Tibet Plateau and the surroundings in spring，summer and autumn over Tibetan Plateau．In winter。the trend of surface air temperature is 0．02，一0．03 and一0．13℃／10 a for 3 zones with elevations in the range of 1．5-2 ian。3—3．5 iun and 4．5—5 ian，respectively．The relatively weak warming revealed in the E】【p．50yrs may be related to the increasing atmospheric aerosol concentration originatedfrom South and East Asia during the past decades．

The method for drought monitoring by remote sensing and monitoring flow were introduced in the paper，which can transfer
NOAA／AVHRR data received from DVBS system to Erads software where geographical correction and image mosaic can be done，and
drought monitoring model can be made and Inn．Drought occul"l~d in four provinces ofNorthwest China in the last ten—day of July，
2006 was monitored by using this method and work flow．an d the results were in agreement with observations of soil moisture in this area．It shows if proper drought monitor model is chosen，the drought magnitude can be monitored by this method and work flow．

The method for drought monitoring by remote sensing and monitoring flow were introduced in the paper，which can transfer NOAA／AVHRR data received from DVBS system to Erads software where geographical correction and image mosaic can be done，and drought monitoring model can be made and Inn．Drought occul"l~d in four provinces ofNorthwest China in the last ten—day of July，2006 was monitored by using this method and work flow．an d the results were in agreement with observations of soil moisture in this area．It shows if proper drought monitor model is chosen，the drought magnitude can be monitored by this method and work flow．

Using 1961一2000 dekadly precipitation from 76 weather stations in the Qinling mountains and the surroundings and largescale grid winds at 850 hPa from NCAR/ NCEP ,the climatology spatial一temporal characteristics of the precipitation and their as sociations with the atmospheric circulation have been analyzed in this paper. The results show that the flood season for the 40一year average occurs in the period from the third dekad of June to the first dekad of October ,during which there are two peaks of precipitation ahe first dekad of July and the first dekad of September. The rainfall in the south side of the Qinling mountains is obviously higher than that in the north side ,although the interannual variations of both are basically consistent. The Qinling mountains and the surroundings are mainly controlled by the southwesterly monsson in the flood season ,e}ecially in the midsummer ,but are mainly impacted by the southeasterly monsoon in the early autumn. The composite analyses show that when theprecipitation is more(less)than normal ,the southerly wind at the south boundary of the study area is often stronger(weaker) than normal in the flood season. By the regression analyses ,it is found that the increased rainfall in a dekad in the flood season generally corresponds to the strengthened Somali
Jet and southwesterly monsoon in the dekad with a two一dekad lead ,and an anomaly anticyclone near Taiwan in the one一dekadlead
dekad and the same dekad.