1. Introduction

The most difficult is that the hydrology science perhaps cannot take the natural objects to laboratory for experimental studies, but the development of hydrology will depend mostly on the field observations and experiments; even the foundation of scientific hydrology recognized by UNESCO in 1974 is not from the work in laboratory but from the two field basin studies in France [1]. The first modern basin studies commenced in Switzerland at Emmental during 1890s; after that, a multitude of basin studies have developed from many parts of the world since the early twentieth century. Following it, a period of rapid development of hydrological basin studies was resulted from the International Hydrology Decade (IHD) Representative and Experimental Basin Program 1965–1974; during this period, it is estimated that ca. 3000 experimental basins (EBs) have been conducted [2]. If we designate the first phase of basin study until ca. the middle twentieth century as the stage of foundational and the second phase during/after the IHD as the stage of developmental, which has been going on for more than five decades up to now, a third phase of renovation seems ready to come out inevitably. A paper coauthored by 12 scientists pointed out that "Yet, most field experiments and observations in watershed science to date, remain largely descriptive..., have not set out to seek fundamental truth or understanding (nor test any formal theory or hypothesis per se)" [3] while Sivapalan alarmed that "catchment hydrology is trapped in a dead-end track, a theoretical impasse" [4], but the field study also meets its risk of decline, more complicated challenges, as Burt and McDonnell asked: "Field work: A dying art?" [5].

Question was then raised that "What's wrong with the status quo" [3]? Yes, there are many objective causes to look for, e.g., "many times things do not work out, weather does not cooperate," "field studies can be difficult to publish in international journals if they are seen as case studies" [5]. "There has been a movement away from field work and towards an almost complete dependence on modeling," as "computing power has become less expensive and field work more expensive (and risky, compared to model approaches)" [6]; this impacts researchers to flinch from field study rather modeling. However, to remind of especially the inherent objective roots have the significance. Learned from Chinese decades' experiences in their field basin studies with zigzagging process [7] especially those based on the concept of experimental basin, the inherent defects have been summarized mainly as the following: (1) designs of the experimental basins have been limited by the black box concept, as well as by many misconceptions (e.g., the linearity, nonheterogeneity, additivity of hydrologic systems, etc.), (2) operation has been substantially bounded by the hydraulic conception of these watersheds as isolated hydrological systems, (3) the studies of experimental basin are focused just on the surface hydrology, and (4) all of these watershed studies monitor only total runoff at the stream-outlet, and the subsurface responses of the watershed are only estimated by hydrograph separation [7, 8].

After the first stage of foundational and the second stage of developmental, if it reveals that experimental watershed hydrology is "inevitably going into a third phase of transition and innovation [8]"? While the planet moves to a new geologic era of Anthropocene [9], what faced is a changing nature of great transition with anthropogenic perturbation, replumbing of the hydrologic cycle [10], and natural climate oscillations. Aimed at the substantial progress in hydrologic science toward "a new unified hydrologic theory" as Sivapalan suggested [4], the answer will certainly be Yes. For this purpose, it, however, "ultimately depends on supporting new experimental work, new field observations, and new data collection networks" [11]. But, what shape will these new experiments and networks take? Twofold is reported here: our exploratory idea and practical tests.
