Assuming the Himalayas are successfully lowered to around 1,000-3,000 meters in altitude with artificial means, with some mountains kept at their actual altitude to feed the most important rivers, the climate becomes much colder (continental climate in the north, subtropical in the middle and tropical in the south) and also drier. Since I don't think temperatures change UV radiations a lot, what would be the necessary changes in geographic conditions (by humans) in order to make UV radiation as weak as in Germany, or preferably the Sichuan bassin?
Artificially simulate a northern-latitude environment in India (UV radiation) in order to make its natives fair-skinned
$\begingroup$ @JohnDallman Oops, I've just changed it. $\endgroup$– BangerbladeMar 12 at 12:32
$\begingroup$ Is it needed that badly? You could also have mass immigration, together with mass extinction if you want it. No need to change geography and weather to get to your goal. $\endgroup$– TrioxidaneMar 12 at 15:11
1$\begingroup$ I believe this intent of this question is too simplistic (but a good question). The average altitude of India is only 621 meters while the average altitude of the U.S. is 763 meters and the avg for Mexico is 1.1 km. By your logic, the average U.S. native should be darker than the average Indian native. I believe more variables are involved, like the day/night ratio of off-equator latitudes. (*Continued*) $\endgroup$– JBHMar 12 at 18:24
$\begingroup$ ... In fact, could somebody with more info about this than I (not too hard, I assure you) comment as to whether or not winter is a more important variable than altitude? I seem to recall that one of the arguments for humanity loosing pigmentation is that snowy climates means short enough days for a large enough portion of the year to affect the need for pigmentation. $\endgroup$– JBHMar 12 at 18:26
1$\begingroup$ India does not really receive all that much more UV radiation than Germany in summer. The difference is that Germany has winter for half a year, and in winter the whole amount solar radiation is lower, not just UV, is lower than in summer. Another difference is that the average elevation of India is about 620 meters ASL, wheres the average elevation of Germany is about 260 meters ASL. There is not much you can do other than eroding India to make it lower, and moving it about 25° northwards. $\endgroup$– AlexPMar 12 at 18:51
India has moved north to its present location from quite a distance south of there. The resulting collision with Asia is what built the Himalayas. If India had stayed south, the UV radiation would be much lower, and the Himalayas would not exist. The Deccan Traps might not be there either as they were acquired as India passed over the Reunion hot spot.
Keeping India south would have made significant differences to the geology and climate.