Table 1. Descriptions of the nine study cities [14].

Site	Landforms	Elevation (m)	Average annual precipitation (mm)	Average annual temperature (°C)	Soil types	Population size (thousand)	City area (km2)	Soil sampling numbers
Shiyan	Mountain	263	800	13.1-16	Yellow brown soil	310	62	42
Enshi	Mountain	425	1000-1200	13.4-16.3	Yellow brown soil	800	80	39
Yichang	Mountain	142	992	13.1-18	Yellow brown soil	557	92	45
Jingmen	Hill	112	949	16.1	Paday soil	680	50	39
Suizhou	Hill	66	865-1070	15.5	Yellow brown soil	650	43	39
Xiangfan	Hill	71	878	15.1-16.9	Yellow brown soil	2230	107	42
Jingzhou	Plain	30	1100-1300	15.9-16.6	Yellow brown soil	1140	66	42
Wuhan	Plain	27	1100	15.8-17.5	Yellow brown soil	5170	500	78
Xiaogan	Plain	26	1112	15.8	Paday soil	950	33	39