Annual Precipitation in Ganga Basin

Annual Precipitation

The weather in the Ganga basin is characterized by a distinct wet season during the period of south west monsoon (June to September). The southwest monsoon makes landfall at the mouth of the Ganga around the first week of June and advances upstream. By the end of July the monsoon reaches the western end of the Ganga basin. In the majority of the basin, the rainy season spreads over three months (July, August and September) and usually 70 to 80% of the total annual rainfall occurs during this period. In the eastern part of the basin, such as in West Bengal and Bihar, the wet season is longer, usually starting in June and continuing until the end of September or early October.

Sub-Basin Wise Annual Rainfall (mm) (1971 - 1987)

Year	1971	1972	1973	1974	1975	1976	1977	1978	1979	1980	1981	1982	1983	1984	1985	1986	1987
Above Ramganga Confluence Sub Basin	1451	915	1121	793	1209	951	1068	1442	809	1163	949	1191	1316	906	1084	992	618
Banas Sub Basin	761	441	945	627	918	774	726	737	556	541	599	630	824	518	506	521	376
Bhagirathi and others (Ganga Lower) Sub Basin	2220	1252	1856	1845	1625	1474	1879	1682	1384	1873	1705	1314	1618	2107	1655	1731	1974
Chambal Lower Sub Basin	1135	654	792	753	1032	851	872	746	538	857	725	950	950	535	889	680	594
Chambal Upper Sub Basin	967	605	1493	777	905	1133	906	969	768	738	848	794	891	898	707	943	635
Damodar Sub Basin	2013	1206	1561	1340	1343	1183	1649	1691	992	1356	1345	1115	1311	1604	1288	1518	1449
Gandak and others Sub Basin	1686	884	1401	1281	1158	1094	1232	1174	957	1468	1267	1010	1219	1487	1400	1447	1576
Ghaghara Confluence to Gomti confluence Sub Basin	1580	788	1017	789	1057	993	1040	1218	750	1336	1019	947	921	1133	1074	1053	1135
Ghaghara Sub Basin	1687	861	1171	953	1293	1011	961	1121	842	1530	1205	1229	1338	1170	1378	1138	949
Gomti Sub Basin	1500	674	1020	774	1194	893	838	1229	807	1415	1024	1157	1125	1052	1124	905	750
Kali Sindh and others up to Confluence with Parbati Sub Basin	1209	697	1293	887	1083	985	959	936	681	821	823	963	971	814	951	1027	802
Ramganga Sub Basin	1494	877	1241	784	1210	1016	1057	1323	748	1239	959	1128	1440	975	1234	994	592
Sone Sub Basin	1609	1116	1166	878	1225	1128	1338	1465	774	1336	1054	1091	1128	1260	1167	1171	1284
Tons Sub Basin	1435	953	1058	743	1241	996	1213	1449	719	1408	962	1062	1057	1120	1028	1040	1035
Upstream of Gomti confluece to Muzaffarnagar Sub Basin	1231	720	919	685	1013	824	1003	1196	664	1156	856	934	982	872	909	831	624
Yamuna Lower Sub Basin	1240	801	983	820	1110	885	1063	1107	608	1233	805	1150	1177	825	1096	889	817
Yamuna Middle Sub Basin	755	600	636	590	826	746	925	707	389	679	635	680	913	529	685	487	323
Yamuna Upper Sub Basin	1194	742	896	727	1055	885	931	1218	671	760	728	943	1011	711	825	752	545
Kosi Sub Basin	1820	762	1483	1575	1234	1348	1242	1176	1128	1449	1409	793	1243	1667	1598	1491	1990
Sub-Basin Wise Annual Rainfall (mm) (1988 - 2004)
Year	1988	1989	1990	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000	2001	2002	2003	2004
Above Ramganga Confluence Sub Basin	1203	946	1282	767	884	1142	974	1073	1080	1130	1354	914	1267	906	918	1196	979
Banas Sub Basin	543	492	729	561	653	537	732	702	774	821	627	556	415	507	300	580	575
Bhagirathi and others (Ganga Lower) Sub Basin	1805	1814	1892	1915	1471	1895	1427	2252	1705	1875	2276	2404	1924	1842	1768	1814	1749
Chambal Lower Sub Basin	725	483	835	680	813	750	805	877	845	853	751	866	635	753	415	725	618
Chambal Upper Sub Basin	837	641	1061	754	689	859	1120	753	1051	973	830	801	496	664	528	829	873
Damodar Sub Basin	1398	1351	1627	1490	1254	1460	1496	1713	1435	1686	1514	1924	1406	1538	1437	1461	1340
Gandak and others Sub Basin	1337	1342	1235	1112	913	1189	1182	1187	1285	1353	1421	1500	1251	1303	1122	1255	1058
Ghaghara Confluence to Gomti confluence Sub Basin	971	1039	1233	962	792	891	1088	951	1024	1145	1077	1184	965	1101	842	1103	573
Ghaghara Sub Basin	1118	1102	1287	916	840	1175	935	994	1076	1121	1308	1001	1276	1022	901	1166	860
Gomti Sub Basin	866	781	1026	882	834	793	770	835	971	988	1030	968	962	877	736	1089	680
Kali Sindh and others up to Confluence with Parbati Sub Basin	832	621	1103	779	765	979	1104	905	1039	1008	831	1008	632	796	578	872	821
Ramganga Sub Basin	1098	906	1345	781	872	1248	855	1092	1019	1081	1362	950	1339	853	1009	1381	904
Sone Sub Basin	997	978	1307	1018	907	1045	1462	1036	1091	1353	1187	1238	971	1312	986	1374	1009
Tons Sub Basin	961	843	1251	980	952	898	1228	954	949	1187	1011	1318	1033	1123	869	1261	821
Upstream of Gomti confluece to Muzaffarnagar Sub Basin	887	623	922	753	773	717	819	802	904	925	985	961	839	774	701	1023	568
Yamuna Lower Sub Basin	908	670	1155	812	927	936	1032	865	994	1015	939	1138	811	925	749	1105	771
Yamuna Middle Sub Basin	751	424	694	512	705	644	631	817	812	736	800	654	516	513	430	780	469
Yamuna Upper Sub Basin	1054	763	1020	642	753	800	919	966	1047	1008	1052	686	839	761	574	778	819
Kosi Sub Basin	1414	1594	1228	1193	956	1450	931	1250	1261	1401	1570	1723	1380	1296	1092	1279	1096

The average annual rainfall for Ganga basin varies from 400 - 2000 mm. The value of rainfall for 34 years (1971-2005) the Ganga basin can be broadly is classified into 11 zones based on the rainfall received in that area. About 27.31% of total area of Ganga basin receives a rainfall of 1000-1200mm, 23.14% area receives 800-1000mm, 15.51% area of the basin receives 600-800mm and 14.29% of basin area receives 1200-1400mm. The trend of monthly average from 1971 to 2004 is given below :

Trend of monthly average rainfall (1971-2004)

The annual average rainfall in the basin varies between 400 - 2000 mm. 80% of the rainfall occurs during the monsoon months i.e. between June and October. Because of large temporal variations in precipitation over the year, there is wide fluctuation in the flow characteristics of the river. The highest rainfall of 1441.26 mm is observed in 1971 and lowest rainfall of 786.57 mm is observed in 1979. The trend line of monthly average rainfall (1971-2004) shows that there is a marginal decrease in average annual rainfall. The average annual rainfall for the basin is estimated as 1059.74 mm.

Within the Ganga basin, every square kilometer of land surface area receives an average of 1 MCM of water annually through rainfall. However, less than half of this is actually available, after accounting for water lost through evapo-transpiration (30%) and seepage into the ground (20%). Since the vast majority is concentrated in a three month span in most of the basin, the water available from rainfall usually exceeds what is lost through evaporation during this period, allowing some surplus water to flow down the Ganga and its tributaries.

Ministry of Rural Development (MoRD), in 2002, has identified the districts and blocks that are affected by drought and declared them as drought prone under Drought Prone Area Programme (DPAP). As per DPAP scheme, the Ganga basin has 76 districts of 9 states are affected by drought (Bihar - 6 districts, Chhattisgarh - 3 districts, Himachal Pradesh - 1 districts, Jharkhand - 14 districts, Madhya Pradesh - 16 districts, Rajasthan - 8 districts, Uttarakhand - 7 districts, Uttar Pradesh - 16 districts, West Bengal - 5 districts).

(1. Source: India-WRIS 2. NGBRA report on Environmental and Social Management Framework)