Previously he was executive officer for the Global Water Systems Project (GWSP) of the Earth System Science Partnership and for the project Biospheric Aspects of the Hydrological Cycle (BAHC) of the Global Environmental Change Programs, senior scientist in the International Dialogue on Water and Climate in the Netherlands, and research analyst for the Advisory Council to the German Government on Global Change (WBGU).

Holger holds a doctoral degree from Potsdam University and a master’s degree from Bayreuth University, Germany in environmental sciences (geo-ecology).