Table 4.

Regression equation of geographical factors (altitude (H), temperature (T), longitude (L_o) and latitude (L_a)) and annual precipitation of meteorological stations in different periods.

Period	Regression equation	R2	P(H)	P(T)	P(Lo)	P(La)
1961–1970	Y = − 0.258 × H − 71.5 × T − 84.9 × Lo + 51.3 × La − 2678.7	0.732	0.025	0.003	0.000	0.011
1971–1980	Y =  − 0.247 × H − 60.7 × T − 93.3 × Lo + 67.1 × La − 2032.7	0.805	0.020	0.001	0.000	0.014
1981–1990	Y =  − 0.228 × H − 55.0 × T − 87.6 × Lo + 70.8 × La − 2646.3	0.826	0.034	0.004	0.000	0.011
1991–2000	Y =  − 0.172 × H − 49.6 × T − 96.2 × Lo + 61.6 × La − 1648.2	0.812	0.050	0.002	0.000	0.007
2001–2010	Y =  − 0.151 × H − 20.7 × T − 79.0 × Lo + 105.6 × La − 2352.4	0.817	0.050	0.004	0.000	0.000
2011–2019	Y =  − 0.175 × H − 36.6 × T − 98.8 × Lo + 73.6 × La − 2445.2	0.702	0.043	0.007	0.001	0.000

Regarding P(H), P(T), P(L_o) and P(L_a) means the result of t test, less than 0.05 indicates that the variable is significant.