it depends where is located the lake and the type of climate. Let's assume that it is in India (right?). So the winter is usually the season of low rainfall and temperatures, which means that the water balance is negative. If the lake level is decreasing down the usual limit it means that either the rainfall recharge during the preceeding summer rain seasons was lower (it can be a cumulative effect over several years, like in the example of the paper I copy to you), and it can also be due to the increase of winter temperatures, mostly due to climate change.
Anyway you need to explore long time series of rainfall and temperatures in the area.
Winter period in this case seem to be a water deficit period and may be indicated by a precipitation of thenardite mineral as a crystals(Na2SO4) along shore line.