Chief Economic Advisor V Anantha Nageswaran on Wednesday said the second half of the current fiscal is going to be challenging because downside risks to global growth have increased and interest rates are rising across the world. He also said the 7.8 per cent GDP growth in the April-June quarter is based on "credible and reliable data" and did not come out of "thin air" as high-frequency data, including GST collection, credit growth and export numbers, indicate continuing economic momentum in the July-August period.