The distribution of CWR is very important to the layout planning of weather modification in China. Based on the reasonable results of China’s CWR, the characteristics of CWR in different weather modification sub-regions are further investigated in this study. The multiyear average values of the annual quantification results of CWR and its related quantities in various regions in the past 20 years are listed in Tables 1 and 2, respectively. In order to remove the influence of the study area on the results, CWR and its components, as well as GMx are converted into the value per unit area (kg m−2, equivalent to mm) for comparison and analysis.
Region GMh CWR GMv Ps Cvh Qhi Qhi − Qho Qvi Qvi − Qvo Es Southeast 2178.7 538.1 20,196.3 1640.7 1728.6 449.9 −27.4 19,224.1 770.4 897.5 Central 1464.4 472.0 13,243.3 992.4 1066.3 397.8 −13.2 12,271.8 102.1 903.1 Southwest 1124.6 247.2 6316.7 877.4 945.6 178.8 −15.5 5836.9 472.6 420.4 Northeast 942.3 350.0 7182.0 592.4 648.4 293.7 12.0 6582.1 51.3 528.9 North 830.7 388.8 9030.0 441.8 495.4 335.1 19.3 8537.1 5.3 417.0 Northwest 445.1 190.3 2651.6 254.8 316.6 128.3 5.5 2421.6 89.6 159.6 China 838.1 176.4 3835.9 661.7 727.1 110.8 −2.6 3347.3 243.8 420.5
Table 1. Multiyear (2000–2019) averaged values of the CWR, GMh, GMv, and other quantities in the six weather modification regions in the Chinese mainland (kg m−2, equivalent to mm water depth per unit area)
Region PEh (%) PEv (%) RTh (h) RTv (day) CEv (%) Southeast 75.1 7.9 3.8 7.8 8.5 Central 67.7 7.3 4.4 9.0 8.0 Southwest 78.0 13.6 4.4 6.3 15.0 Northeast 62.6 8.0 5.8 7.8 9.0 North 53.1 4.7 5.8 10.0 5.5 Northwest 57.3 9.4 9.1 12.4 11.9 China 78.9 17.2 5.1 8.1 18.9
Table 2. Multiyear (2000–2019) averaged value of the conversion efficiency and renewal time of water vapor and hydrometeors in the atmosphere in the six weather modification regions of China. The variables PEh and PEv refer to the precipitation efficiency of hydrometeors and water vapor, respectively (%); RTh and RTv refer to the renewal time of hydrometeors and water vapor with the unit of hour and day, respectively; and CEv refers to the condensation efficiency of water vapor (%)
According to Table 1, in the past 20 years, GMh per unit area in each region can be sorted from high to low as follows: southeast region (2178.7 mm), central region (1464.4 mm), southwest region (1124.6 mm), northeast region (942.3 mm), north region (830.7 mm), and northwest region (445.1 mm). The variable GMh in the southeast region is almost five times of that in the northwest region. The regional characteristics of annual Ps are consistent with GMh, being the most in the southeast region (1640.7 mm), followed by the central region (992.4 mm), the southwest region (877.4 mm), the northeast region (592.4 mm), and the north region (441.8 mm). The annual Ps is the least in the northwest region (254.8 mm). After deducting Ps, the annual CWR remaining in the atmosphere can be sorted from high to low as follows: southeast region (538.1 mm), central region (472.0 mm), north region (388.8 mm), northeast region (350.0 mm), southwest region (247.2 mm), and northwest region (190.3 mm). In other words, CWR is more in the south and the east, less in the north and the west. The variable GMv in each region is generally one order of magnitude higher than GMh, and it can be sorted from highest to lowest as: southeast, central, north, northeast, southwest, and northwest regions. Its regional distribution is different from that of GMh but is consistent with that of CWR.
From the comparison of GMh and CWR in Table 1, it can be seen that on average over many years, Cvh in each region contributes the most to GMh and CWR in the region, and is slighter higher than Ps in the region. The order among different regions is consistent with the annual Ps, i.e., the highest in the southeast region (1728.6 mm), followed by the central region (1066.3 mm), the southwest region (945.6 mm), the northeast region (648.4 mm), and the north region (495.4 mm), and the least in the northwest region, only 316.6 mm.
The regional deviation of Qhi is smaller than that of Cvh. The variable Qhi is still the highest in the southeast region and the lowest in the northwest region. The annual Qhi in the other four regions can be listed from high to low as: the central, north, northeast, and southwest regions. The rank of Qvi in each region is consistent with Qhi, but Qvi is generally higher than Qhi by a few dozen times. The water vapor advection in each region is expressed as a net inflow (that is, water vapor convergence), and the order from high to low is: southeast, southwest, central, northwest, northeast, and north regions, with the value in the southeast region 127 times of that in the north region. Atmospheric hydrometeor advection in the six regions is different. Hydrometeors in the north, northeast, and northwest regions all show regional convergence (i.e., Qhi > Qho), while those in the central, southwest, and southeast regions show regional divergence (i.e., Qhi < Qho).
Detailed analysis shows that there is a good correlation between the annual water vapor convergence and the annual Ps in the same region with the correlation coefficient reaching 0.85. In other words, the more water-vapor convergence, the higher Cvh, which in turn triggers more Ps, such as in the southeast and southwest regions.
In addition, Table 1 also presents the results of Es. Among the six regions, the central region has the largest Es, with an annual mean value of 903.1 mm. The annual Es in the southeast region is about 897.5 mm, only second to that in the central region, followed by the northeast region (528.9 mm), southwest region (420.4 mm), north region (417.0 mm), and northwest region (159.6 mm). Combined with the annual Ps, it can be seen that the annual Ps is significantly higher than Es in the southeast, southwest, and northwest regions, and Ps in the central, northeast, and north regions is slightly higher than the regional Es.
In general, for regional CWR quantification, Cvh makes the largest contribution to GMh and CWR. As for the 1° × 1° gridded CWR quantification in North China presented by Cai et al. (2020), the contribution of Qhi to GMh and CWR is more important. The reason is that advection cancels each other out within a large area, and only the advection on the boundary is counted, so the effect of the advection terms is weakened (see Section 5.1 for details). Therefore, for atmospheric hydrometeors, the contribution of advection and source/sink terms to GMh is affected by the spatial scale, and there are obvious differences between different spatial scales. However, no matter the quantification is based on 1° interval grids or the overall region, the contribution of Qvi to GMv is the highest, which is different from atmospheric hydrometeors.
According to Table 2, the multiyear average values of annual PEh in the six regions are ordered as follows: southwest region (78.0%), southeast region (75.1%), central region (67.7%), northeast region (62.6%), northwest region (57.3%), and north region (53.1%). For RTh, the order from short to long is: southeast region (3.8 h), central and southwest regions (4.4 h), north and northeast regions (5.8 h), and northwest region (9.1 h). Besides, PEv in each region is smaller than PEh, and RTv longer than RTh. The rankings of PEv and RTv for different regions are slightly different from those of PEh and RTh, but in general, PE is high and RT is short in the southeast and southwest regions, while low and slow in north and northwest regions.
The condensation from water vapor to hydrometeors is mainly affected by terrain uplift and local water vapor content. Therefore, the southwest region with complex terrain has the highest CEv (about 15.0%), followed by northwest region (11.9%), northeast region (8.9%), southeast region (8.5%), and central region (8.0%). The north region has main plains and therefore has the lowest CEv of only 5.5%.
Among the six regions, the southeast region has a relatively large GMh. Although the clouds in the southeast region have a higher precipitation efficiency, there are still a large part of the hydrometeors remaining in the air which can be developed and utilized by artificial weather modification. Therefore, CWR in the southeast region is also the most abundant. In the northwest and north regions, GMh is relatively small but PEh is low, so there is still a certain amount of CWR available for development and utilization.
Figure 7 presents the interannual variation of CWR and its related quantities in the six sub-regions from 2000 to 2019. The CWR-related quantities in various regions in the past 20 years have shown a fluctuation trend. Specifically, two groups of quantities, i.e., annual Ps and Cvh, annual Qhi and CWR, show similar interannual variation characteristics.
Figure 7. Interannual variations of CWR and its related quantities in the six weather modification regions in China from 2000 to 2019. (a–f) represent the southeast, southwest, central, north, northeast, and northwest regions, respectively. All the values are annual results.
The interannual variation of Ps in the southeast region (Fig. 7a) is very dramatic. The variable Ps in the wet year (2016, with an annual Ps of 2157.8 mm) was almost double that in the dry year (2011, 1247.5 mm). The variable PEh was the lowest in 2011 (68.7%). In other years, PEh generally exceeded 70%. In the southwest region (Fig. 7b), the interannual variation of Ps was not obvious, but Ps and PEh decreased slightly in the past 20 years. In 2009, Ps and PEh were only 748.3 mm and 74.8%, respectively. In the central, north, northeast, and northwest regions (Figs. 7c–f), the lowest values of Ps all occurred in 2001. Specifically, Ps in the northwest region showed an increase trend. The variable PEh of the above four regions in the past 20 years generally fluctuated. Among them, PEh in north and northwest regions kept stable during 2000–2010 and increased after 2010. The variable PEh continuously increased since 2001 in the northeast region. In the central region, PEh decreased slightly before 2011, but there were multiple peaks in the past 10 years.
In the southeast, southwest, north, and northwest regions, CWR and Qhi increased in volatility since 2000, reached a peak value in 2010, and then decreased in volatility. CWR and Qhi in the central region showed a quasi-7-yr periodic variation, while the interannual variations of CWR and Qhi in the northeast region were the most obvious.
Using the observation data from the national meteorological stations from 1956 to 2013, Ren et al. (2015) analyzed the variation trend of precipitation in China, and they pointed out that the decrease of annual precipitation mainly occurred in North China and Southwest China, while the annual precipitation increased obviously in Northwest China and other regions. Their results are quite consistent with our conclusions.
Figure 8. Multiyear (2000–2019) averaged monthly variations of CWR and its related quantities in the six weather modification regions in China. (a–e) represent GMh, Cvh, Ps, CWR, and Qhi, respectively. All the values are multiyear averaged monthly results.
Figure 9. Multiyear (2000–2019) averaged monthly variations of (a) PEh (%) and (b) RTh (h) of the six weather modification regions in China. All the values are multiyear averaged monthly results.
(1) CWR and its components
The monthly Cvh in each region is generally slightly higher than the regional Ps, and the trends of the two are similar. In the monthly variation curves of Cvh and Ps in the southeast region, there are multiple peaks, and the main peak appears in June (Cvh and Ps are 292.7 and 285.4 mm, respectively) with other small peaks in August and November. Cvh and Ps in the other five regions all present a single peak distribution, with the peak of Ps in July. In general, Ps is higher in the central region, and is lower in the northwest region.
The monthly Qhi in different regions is generally less than Cvh and Ps in the same month. The monthly variations of Qhi have obvious seasonal characteristics. In the southwest, northeast, north, and central regions, Qhi is the highest in summer, followed by spring and autumn, and the least in winter. In the southeast and northwest regions, Qhi is the highest in spring. In the southeast region, Qhi in the first half of the year is significantly higher than in the second half, and the monthly mean Qhi is the highest among the six regions. In the other five regions, the monthly variation of Qhi in spring and autumn is relatively small. The variable Qhi in each month in the central region is generally higher, followed by the north, northeast, southwest, and northwest regions.
Affected by the monthly variations of Cvh, GMh in the southeast region has a multipeak distribution throughout the year, with the highest peak in June (close to 350 mm) and small peaks in August and November. In July, GMh in the southeast region is slightly lower than that in the central region, while in other months GMh in the southeast region is generally higher than that in other regions. Except for the southeast region, the monthly variations of GMh in other regions present a single-peak distribution. That is, GMh begins to increase from January, reaches the peak value in July, and then decreases gradually. The monthly GMh of the central region is higher than that of other regions in the same month, and the monthly variation and deviation are more obvious (50–250 mm). The monthly GMh in the northwest region is the lowest, and the monthly variation is relatively small (20–60 mm).
The monthly variation curve of CWR is relatively similar to that of Qhi. CWR in winter is the least throughout the year in the six regions. In the southeast and northwest regions, the most abundant CWR is in spring, while in the other four regions CWR is more abundant in summer. In the southwest region, CWR in summer is significantly higher than that in autumn by about 30%. In other regions, the CWR in spring and autumn is close to that in summer, with the deviation ranging from 0.6% to 21%.
(2) PEh and RTh
In the past 20 years, the monthly variation of PEh in six regions is consistent with that of precipitation. The highest PEh is in summer (65%–88%), followed by autumn (25%–82%) and spring (20%–78%), and the lowest value is in winter (14%–65%). Except the southeast region, PEh in other five regions all reaches their peak in July. The difference of PEh in different months in the northeast and north regions is large, and the seasonal difference is more obvious. In the northeast region, PEh is close to 80% in summer and less than 30% in winter; in the north region, PEh can reach 70% in July but less than 15% in December. In the southeast region, PEh exceeds 80% in summer, and the values in June and August are slightly higher than in July.
The monthly variation of RTh is opposite to that of PEh, with the shortest RTh in summer and the longest RTh in winter. In the southeast, southwest, and central regions, the monthly variation of RTh is relatively small. In these regions, RTh is only about 3 h in summer and less than 15 h in winter. In the northeast, northwest, and north regions, the seasonal differences of RTh are quite obvious. Taking the north region as an example, RTh is 3–4 h in summer and dozens of hours in winter. RTh is closely related to Mh and monthly precipitation in different regions and different months. Since precipitation in each region is the highest in summer and the lowest in winter throughout the year, it can be inferred that Mh in each region is also the largest in summer and the least in winter.
|Region||GMh||CWR||GMv||Ps||Cvh||Qhi||Qhi − Qho||Qvi||Qvi − Qvo||Es|