Consider people living between tropic of cancer to tropic of capricon - that is, within 23.5degrees close to equator. They have two summers (summer is the time of the year at which sun is closest to that location). When sun travels from south to north and viceversa.
Now think about people in Kerala, they are 10deg north of equator. On March 21 sun is shining directly above equator. Then around April 15 sun reaches directly above Kerala on its travel to north. This is the first summer of the year for kerala. Sun will continue travel north till Gujarat(it is on tropic of cancer). On June 21 when sun is shining over tropic of cancer, it is 13deg north of kerela.
Then it will start its travel south. Around Aug 31 sun will be directly above kerala again. This is the second summer of the year. The summers are only 4 months apart.
For somebody in Kenya (on equator) there will be two summers and winters in an year and they will be exactly 6 months apart. So for them half year will be more important measure of time than an year for those live north or south of respective tropics.
The eliptical orbit of earth around sun does not have much effect on these summers. In this orbit, earth is closest to sun on Jan 4; farthest on Jul 4. Both the Kerala summer points are around 3.5 & 4 months away from Jan4 (closest day).