mid summers ( southwest monsoon , June to September ) ; less cloudy , scant rainfall , mild temperatures , lower humidity during winter ( northeast monsoon , December to April ) Terrain : central lowlands ringed by steep , rugged highlandsNatural resources : petroleum , timber , tin , antimony , zinc , copper , tungsten , lead , coal , some marble , limestone , precious stones , natural gasLand use : arable land : 15 % permanent crops : 1 % meadows and pastures : 1 % forest and woodland : 49 % other : 34 % Irrigated land : 10 , 180 sq km ( 1989 ) Enviro